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THE  MACMILLAN  COMPANY 

NEW  YORK    •    BOSTON    •    CHICAGO 
DALLAS   •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  Limited 

LONDON  •  BOMBAY  •  CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  Ltd. 

TORONTO 


COLLEGE   ZOOLOGY 


BY 


ROBERT   W.    HEGNER,   Ph.D. 

ASSISTANT   PROFESSOR   OF   ZOOLOGY   IN   THE   UNIVERSITY 
OF  MICHIGAN 


THE    MACMILLAN    COMPANY 
1912 


Copyright,  1912, 
By  the  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.    Published  July, 


1912. 


Norfajooti  iPresg 

J.  8.  Cashing  Co.  —  Berwick  &  Smith  Co. 

Norwood,  Mass.,  U.S.A. 


QL47 
191?. 


PREFACE 

This  book  is  intended  to  serve  as  a  text  for  beginning  students 
in  universities  and  colleges,  or  for  students  who  have  already 
taken  a  course  in  general  biology  and  wish  to  gain  a  more  com- 
prehensive view  of  the  animal  kingdom.  It  differs  from  many 
of  the  college  textbooks  of  zoology  now  on  the  market  in  several 
important  respects :  (i)  the  animals  and  their  organs  are  not 
only  described,  but  their  functions  are  pointed  out ;  (2)  the  ani- 
mals described  are  in  most  cases  native  species ;  and  (3)  the 
relations  of  the  animals  to  man  are  emphasized.  Besides  serv- 
ing as  a  textbook,  it  is  believed  that  this  book  will  be  of  interest 
to  the  general  reader,  since  it  'gives  a  bird's-eye  view  of  the 
entire  animal  kingdom  as  we  know  it  at  the  present  time. 

Within  the  past  decade  there  has  been  a  tendency  for  teachers 
of  zoology  to  pay  less  attention  to  morphology  and  more  to 
physiology.  As  a  prominent  morphologist  recently  said, 
"Morphology'  ...  is  no  longer  in  favor  .  .  .  and  among 
a  section  of  the  zoological  world  has  almost  fallen  into  dis- 
grace "  (Bourne).  The  study  of  the  form  and  structure  of 
animals  is,  however,  of  fundamental  importance,  and  is  abso- 
lutely necessary  before  physiological  processes  can  be  fully 
understood ;  but  a  course  which  is  built  up  on  the  "  old-fash- 
ioned morphological  lines  "  is  no  longer  adequate  for  the  presen- 
tation of  zoological  principles. 

In  writing  this  book  the  author  has  attempted,  not  only  to 
describe  the  most  important  structural  features  of  the  various 
types  of  animals,  but  also  to  point  out  the  vital  phenomena  as 
expressed  in  the  functions  of  the  organs.  Furthermore,  an 
endeavor  has  been  made  to  compare  the  animals  in  each  phylum 
with  those  of  the  members  of  nearly  related  phyla,  so  that  the 


VI  PREFACE 

student  may  realize  the  unity  as  well  as  the  variety  in  animal 
life. 

So  far  as  possible  in  a  limited  space,  the  relations  of  the 
animals  to  other  animals,  to  plants,  and  to  environmental 
factors  in  general  are  considered,  and  the  animals  of  special 
economic  importance  are  emphasized.  By  this  method  the 
student  is  brought  into  closer  contact  with  and  gains  a  broader 
idea  of  natural  phenomena.  Questions  naturally  arise  in  the 
student's  mind,  such  as,  "  Where  does  the  animal  live  ?  "  "  What 
does  the  animal  do?"  and  "  What  is  this  or  that  particular 
organ  for?  "  and  stimulate  interest  in  the  work  leading  to  more 
careful  observations  and  more  accurate  inferences. 

Each  phylum  is  introduced  by  a  more  or  less  complete  account 
of  the  anatomy,  physiology,  and  ecology  of  one,  or  in  certain 
cases,  two  or  more  types.  These  types  were  selected  with  the 
following  requirements  in  mind :  (i)  they  must  represent  as 
nearly  as  possible  an  average  of  the  phylum;  (2)  they  must 
illustrate  clearly  the  characteristics  of  the  phylum  so  as  to  serve 
as  an  introduction  to  a  comparative  study  of  other  members  of 
the  group ;  (3)  they  must  be  common  native  species  which  can 
be  obtained  for  direct  observations  in  the  laboratory ;  (4)  they 
must  occupy  an  important  position  in  the  animal  series ;  and 
(5)  they  must  be  of  special  importance  to  man.  Very  few  types 
fulfill  all  of  these  requirements ;  in  several  cases  two  types  have 
been  employed  because  one  was  not  considered  adequate. 

It  is  impossible  in  one  small  volume  to  describe  as  many 
different  animals  under  each  phylum  as  might  be  desired,  or 
to  give  a  full  classification  of  each  group.  However,  a  general 
idea  of  the  various  kinds  of  animals  and  their  habitats  can  be 
obtained  from  the  •  short  account  included  in  each  chapter. 
The  species  mentioned  are  in  most  cases  the  commonest  and 
most  representative  of  those  living  in  North  America. 

More  space  has  been  devoted  to  the  Chordata  than  to  any 
other  phylum,  and  the  classes  under  the  subphylum  Verte- 
brata  have  been  treated  in  a  somewhat  different  manner  from 
those  of   the  invertebrates.     It  is  customary  in  studying  the 


PREFACE  vii 

vertebrates  to  select  one  species  as  a  type  to  be  examined  in 
considerable  detail,  and  then  to  compare  species  belonging 
to  the  other  classes  with  it.  The  animal  usually  chosen  for 
detailed  study  is  the  frog,  and  this  form  has  therefore  been 
treated  more  fully  in  this  book  than  any  other  vertebrate  type. 
The  vertebrates  are,  as  a  rule,  larger  than  the  invertebrates, 
are  fewer  in  number,  and  are  usually  more  interesting  to  be- 
ginning students ;  they  are,  on  the  whole,  better  known  than 
the  invertebrates  and  more  easily  observed.  For  these  reasons 
they  have  been  discussed  largely  from  the  natural  history  stand- 
point, and  it  is  hoped  that  this  treatment  will  give  students 
a  better  idea  of  the  everyday  events  in  the  lives  of  the  more 
common  vertebrates  than  can  be  obtained  from  a  purely  morpho- 
logical course. 

A  book  covering  such  a  large  field  as  this  one  must  necessa- 
rily be  more  or  less  of  a  compilation,  and  the  facts  and  figures 
must  be  selected  from  numerous  textbooks  and  scientific  peri- 
odicals. The  sources  from  which  the  author  has  obtained  a 
large  part  of  his  material  are  as  follows ;  — 

Bourne,  G.  C.      Coinparative  Anatomy  of  Animals^  2  vols.,  1909. 
Bronn,  H.  G.     Klassen  und  Ordnungen  des  Tierreichs. 
Calkins,  G.  N.     Protozoa,  1901. 

Protozoology,  1909. 

CafTibridge  Natural  History,  10  vols. 
Dean,  B.     Fishes,  Living  and  Fossil,  1895. 
Dickerson,  M.  C.     The  Frog  Book,  1907. 
Ditmars,  R.  L.     The  Reptile  Book,  1907. 

Reptiles  of  the  World,  19 10. 

Flower,  W.  H.,  and  Lydekker,  R.     Mammals,  Living  and  Ex- 
tinct, 1 89 1. 
Hertwig,  R.     Manual  of  Zoology,  1905. 
Holmes,  S.  J.     Biology  of  the  Frog,  1906. 
Jennings,  H.  S.     Behavior  of  the  Lower  Organisms,  1906. 
Jordan,  D.  S.      Guide  to  the  Study  of  Fishes,  2  vols.,  1905. 

and  Evermann,  B.  W.     Fishes  of  North  America,  4  vols., 

1900. 


Vlll  PREFACE 

Kellogg,  V.  L.     American  Insects^  1905- 

Kingsley,  J.  S.      Textbook  of  Vertebrate  Zoology,  1899. 

Knowlton,  F.  H.     Birds  of  the  World,  1909. 

Korschelt,  E.,  and  Heider,  K.     Textbook  of  the  E?nbryology  of 

hiverteb rates,  4  vols.,  1895. 
Lang,  A.     Comparative  Anatomy  of  Invertebrates. 
Lankester,  E.  R.     A  Treatise  on  Zoology,  1900-1909. 
Marshall,  A.  M.,  and  Hurst,  C.  H.     Practical  Zoology,  1905. 
Matthew,  W.  D.     Evolution  of  the  Horse.     American  Museum 

Journal,  Vol.  III.     Guide  Leaflet  No.  9,  1903. 
Morgan,  T.  H.     Regeneration,  1901. 
Osborn,  H.  F.     The  Age  of  Mammals,  19 10. 
Parker,  T.  J.     Zootomy,  1884. 
and  Parker,  W.  N.     An  Eleinentary   Course  in  Practical 

Zoology,  1908. 

and  Haswell,  W.  A.     Textbook  of  Zoology,  19 10. 

Schmeil,  O.     Textbook  of  Zoology,  1901. 

Sedgwick,  A.     Student's  Textbook  of  Zoology,  3  vols.,  1 898-1 909. 

Sedgwick,  W.  T.,  and  Wilson,  E.  B.     General  Biology,  1899. 

Shipley,  A.  E.,  and  MacBride,  E.  W.     Zoology,  1904. 

Simpson,  G.  B.     Anatomy  and  Physiology  of  Polygyra  Albolabris 

and  Liniax  Maximus.     Bui.  N.  Y.  State  Mus.,  Vol.  8,  1901. 
Stone,  W.,  and  Cram,  W.  E.     American  Animals,  1905. 
United  States  Department  of  Agriculture.     Circulars  and  Bul- 
letins. 
Verworn,  M.      General  Physiology,  1899. 
Wiedersheim,  R.,  and  Parker,  W.  N.      Comparative  Anatomy  of 

Vertebrates,  1907. 
Wilder,  H.  H.     History  of  the  Human  Body,  1909. 
Willey,  A.     Ajnphioxus   and  the   Ancestry    of   the    Vertebrates, 

1894. 
Williams,  L.  W.     Anato?ny  of  the  Common  Squid.      American 

Museum  of  Natural  History. 
Wilson,  E.  B.     The  Cell  in  Development  and  Inheritance,  1900. 
Zittel,  K.  von.     Textbook  of  Paleo7itology,  2  vols.,  1902. 


PREFACE  ix 

In  an  endeavor  to  avoid  as  many  errors  as  possible,  the 
manuscript  of  most  of  the  chapters  has  been  read  by  zoologists 
who  are  authorities  in  the  special  field  treated  therein.  It  is 
a  great  pleasure  to  thank  these  gentlemen  in  this  place  for  the 
invaluable  assistance  they  have  rendered.  I  am  indebted  to 
Professor  A.  S.  Pearse  for  reading  Chapters  I-IX  ;  to  Mr.  Peter 
Okkelberg  for  reading  the  entire  manuscript ;  to  Professor  G.  N. 
Calkins  for  reading  Chapter  II ;  to  Professor  H.  V.  Wilson  for 
reading  Chapter  IV ;  to  Professor  Charles  W.  Hargitt  for  read- 
ing Chapters  V  and  VI ;  to  Professor  W.  C.  Curtis  for  reading 
Chapters  VII  and  IX  ;  to  Dr.  G.  R.  La  Rue  for  reading  Chapter 
VII ;  to  Dr.  B.  H.  Ransom  for  reading  Chapter  VIII ;  to  Dr. 
Hubert  Lyman  Clark  for  reading  Chapter  X ;  to  Professor 
J.  Percy  Moore  for  reading  Chapter  XI ;  to  Mr.  H.  B.  Baker 
for  reading  Chapter  XII ;  to  Professor  A.  E.  Ortmann  for  read- 
ing the  part  of  Chapter  XIII  relating  to  the  Crustacea,  Ony- 
chophora,  and  Myriapoda  ;  to  Professor  Vernon  L.  Kellogg  for 
reading  the  part  of  Chapter  XIII  relating  to  Insecta  ;  to  Mr.  J.  H. 
Emerton  for  reading  the  part  of  Chapter  XIII  relating  to  the 
Arachnida ;  to  Professor  Alexander  G.  Ruthven  for  reading 
Chapters  XIV-XIX  ;  to  Professor  B.  M.  Allen  for  reading  Chap- 
ter XIV ;  to  Mr.  R.  E.  Richardson  for  reading  Chapters  XV- 
XVII ;  to  Professor  Lynds  Jones  for  reading  Chapter  XX ;  and 
to  Mr.  Marcus  W.  Lyon,  Jr.,  and  Mr.  N.  Hollister  for  reading 
Chapter  XXI.  I  am  also  indebted  to  Dr.  A.  F.  Shull  for  read- 
ing a  large  part  of  the  proof,  and  to  my  wife  for  her  especially 
valuable  assistance  in  reading  proof  and  preparing  the  index. 

ROBERT   W.    HEGNER. 

May  14,  1912. 


CONTENTS 


Preface     

Table  of  the  Classification  of  the  Animal  Kingdom 


PAGE 
V 


CHAPTER   I 


Introduction 


1 .  General  Survey  of  the  Animal  Kingdom  . 

2.  Living  Matter  contrasted  with  Non-living  Matter 

3.  The  Physical  Basis  of  Life  —  Protoplasm 

4.  The  Origin  of  Life   ...... 

5.  The  Cell  and  the  Cell  Theory  .... 

6.  Plants  contrasted  with  Animals 

7.  Classification    ....... 

8.  The  Principal  Phyla  of  the  Animal  Kingdom  . 

9.  Zoology  and  its  Subsciences     .... 


I 

I 
8 

10 
12 
12 
18 
21 
23 
25 


CHAPTER   II 

Phylum  Protozoa 27 

1.  Class  I.     Rhizopoda  .         .         .         .         .        .         .27 

a,  A?neba  proteus^  2j  ;  b,  Rhizopoda  in  General,  39.  t 

2.  Class  II.     Mastigophora 41 

a,  Eiiglena  viridis,  41  ;  b,  Mastigophora  in  General,  45. 

3.  Class  III.     Sporozoa 48 

a,  Monocystis,  48 ;  b,  Plasmodium  vivax,  50 ;  c,  Sporo- 
zoa in  General,  52. 

4.  Class  IV.     Infusoria 53 

a,  Parainechnn  candatum,  53  ;  b,  Infusoria  in  General, 
62. 

5.  Protozoa  in  General  .         .         .         .         .         .         -65 

6.  Pathogenic  Protozoa         .......       70 


Xll 


CONTENTS 


CHAPTER   III 

An  Introduction  to  the  Metazoa 

1 .  Germ  Cells  and  Somatic  Cells  . 

2.  Tissues 

3.  Organs  and  Systems  of  Organs 

4.  Reproduction  .... 

5.  The  Forms  of  Animals     . 


PAGE 

73 
74 
76 

79 
90 


CHAPTER   IV 


Phylum  Porifera 

1 .  Structure  of  a  Simple  Sponge  —  Leucosolenia 

2.  Anatomy  and  Physiology  of  Grant ia 

3.  The  Fresh-water  Sponge  —  Spongilla 

4.  Sponges  in  General ..... 


92 
92 

94 
98 

99 


CHAPTER   V 

Phylum  Ccelenterata 108 

1.  The  Fresh-water  Polyp  —  Hydra 108 

2.  Class  I.     Hydrozoa 118 

a,  A  Colonial  Hydrozoon  —  Obelia,  119;  b,  Metagene- 
sis, 122  ;  c,  A  Jellyfish  or  Medusa —  Gonionemus,  122  ; 
d,  Hydroid  and  Medusa  Compared,  124  ;  e,  Polymor- 
phism, 126;  f,  Reproduction  in  the  Hydrozoa,  127; 
g,  Classification  of  the  Hydrozoa,  128. 

3.  Class  II.     Scyphozoa 129 

a,  A  Scyphozoan  Jellyfish  —  Aitrdia^  129;  b.  Classifi- 
cation of  the  Scyphozoa,  132. 

4=    Class  III.     Anthozoa 133 

a,  A  Sea  Anemone  —  Metridium,  134 ;  b,  A  Coral  Polyp, 
137  i  c,  Coral  Reefs  and  Atolls,  138  ;  d.  Classification 
of  the  Anthozoa,  139. 
5.    Coelenterates  in  General  .         .         .         .         .         .         .142 

CHAPTER  VI 


Phylum  Ctenophora 


145 


CONTENTS  Xlll 
CHAPTER   VII 

PAGE 

Phylum  PlatyhelmixVTHes 150 

1.  A  Fresh-water  Flatworm  —  Flanaria         .         .         .         .150 

2.  Class  I.     Turbellaria 155 

3.  Class  II.     Trematoda                 » 157 

a,  The  Liver  Fkike  —  Fasctola  hepatica^  157;  b,  Tre- 
matoda in  General,  161. 

4.  Class  III.     Cestoda 163 

a,  The  Tapeworm —  Tcenia,  163  ;  b,  Cestoda  in  General, 
165. 

5.  Fhtworms  in  General 166 

CHAPTER   VIII 

Phylum  Nemathelminthes .  169 

1.  A  Parasitic  Round  Worm  —  Ascaris  lumbricoides     .         .169 

2.  Nemathelminthes  in  General    .         .         .         .         .         -173 

CHAPTER   IX 

Invertebrates  of   More  or   Less  Uncertain   Systematic 

Position 176 

1.  Mesozoa  .         .         .         .         .         .         .         .         .         .176 

2.  Nemertinea 177 

3.  Nematomorpha 179 

4.  Acanthocephala 180 

5.  Chaetognatha 180 

6.  Rotifera 181 

7.  Bryozoa 183 

8.  Phoronidea 185 

9.  Brachiopoda 185 

10.    Gephyrea .         .  186 

CHAPTER  X 

Phylum  Echinodermata 189 

1.  Anatomy  and  Physiology  of  the  Starfish — Asterias          .  190 

2.  Class  I.     Asteroidea  —  Starfishes 198 


XIV 


CONTENTS 


3.  Class  II.     Ophiuroidea — Brittle  Stars 

4.  Class  III.     Echinoidea — Sea  Urchins 

5.  Class  IV.   Holothurioidea  —  Sea  Cucumbers 

6.  Class  V.     Crinoidea  —  Sea-lilies  or  Feather-stars 

7.  Development  of  Echinoderms  .... 

8.  Artificial  Parthenogenesis         .... 

9.  The  Position  of  Echinoderms  in  the  Animal  Kingdom 


PAGE 
199 

202 
205 
208 
210 
212 
213 


CHAPTER   XI 


Phylum  Annelida     . 

1 .  The  Earthworm  —  Lninbricus 

2.  Classification  of  Annelids 

3.  Class  I.     Archiannelida    . 

4.  Class  II.     ChaBtopoda 

5.  Class  III.     Hirudinea 

6.  Annelids  in  General 


215 
215 
231 
232 

233 
236 
240 


CHAPTER  XII 

Phylum  Mollusca 242 

1.  The    Pearly  P^esh-water    Mussel  —  Anodonta    and    the 

Uniones 243 

2.  Class  I.     Amphineura 251 

3.  Class  II.     Gastropoda 252 

a,  A  Land-snail,  253  ;  b,  Gastropoda  in  General,  258. 

4.  Class  III.     Scaphopoda 261 

5.  Class  IV.     Pelecypoda  .         .         .         .         .         .         .  261 

6.  Class  V.     Cephalopoda 264 

a.  The  Common  Squid  —  Loligo^  264 ;  b,  Cephalopoda 
in  General,  267. 

7.  Mollusca  in  General 269 

CHAPTER  XIII 

Phylum  Arthropoda        .        .        .        •    .     •        •        •        •     274 
I.    Introduction    .         .         .         .         .         .        .         .         ,     274 


CONTENTS  XV 

PAGE 

2.  Class  I.     Crustacea  .         .         .         .         .         .         .     276 

a,  The  Crayfish  —  Cambarus^  2^6 ;  b,  Crustacea  in 
General,  292. 

3.  Class  II.     Onychophora 305 

4.  Class  III.     Myriapoda 308 

5.  Class  IV.     Insecta 312 

a,  The  Honey-bee,  312;  b,  The  Anatomy  and  Physi- 
ology of  Insects  in  General,  328;  c,  General  Survey 
of  the  Orders  of  Insects,  336 ;  d,  The  Economic  Im- 
portance of  Insects,  370. 

6.  Class  V.     Arachnida 371 

a,  The  Spiders,  371  ;  b,  Other  Arachnida,  377. 


CHAPTER  XIV 


Phylum  Chordata:  Introduction. 

1.  Subphylum  I.     ENTEROPNEUSTA 

2.  Subphylum  II.     TUNICATA       .... 

3.  Subphylum  III.     Cephalochorda    . 

4.  Subphylum  IV.     VERTEBRATA  :  INTRODUCTION 

CHAPTER  XV 


386 
386 
389 

393 
400 


Subphylum  Vertebrata:  Class  I.     Cyclostomata    .        .        .  414 

1.  The  Lamprey — Petromyzon     .         .         .         .         .         -415 

2.  Cyclostomata  in  General .         .         .         .         .         .         .  420 

CHAPTER  XVI 

Subphylum  Vertebrata  :  Class  II.     Elasmobranchii  :     .         .  422 

1.  The  Dogfish-Shark — Squalus  acafithias  .         .         .         .  422 

2.  Elasmobranchs  in  General        ......  428 

3.  The  Economic  Importance  of  Elasmobranchs  .         .         .  431 

CHAPTER   XVII 

Subphylum  Vertebrata:  Class  III.    Pisces    ....  432 

1 .  A  Bony  Fish  —  The  Perch 432 

2.  An  Abridged  Classification  of  Living  Fishes     .         .         .  443 


XVI  CONTENTS 


PAGE 


3.  The  Anatomy  and  Physiology  of  Fishes  in  General  .  445 

4.  General   Account  of  Some  of  the  Principal  Groups  of 

Fishes 4^2 

5.  Deep  Sea  Fishes 472 


6.    Fossil  Fishes 


474 


7.   The  Economic  Importance  of  Fishes        ....     474 


CHAPTER  XVIII 

SuBPHYLUM  Vertebrata:  Class  IV.     Amphibia 

1 .  The  Frog 

2.  A  Brief  Classification  of  Living  Amphibia 

3.  Review  of  the  Orders  and  Families  of  Living  Amphibia 
4..    General  Remarks  on  Amphibia         .... 


477 
477 
510 
512 
522 


CHAPTER   XIX 

SuBPHYLUM  Vertebrata:  Class  V.     Reptilia  ....  527 

1.  The  Turtle 527 

2.  A  Brief  Classification  of  Living  Reptilia  ....  534 

3.  Review  of  the  Orders  and  Families  of  Living  Reptiles       .  540 

4.  The  Poisonous  Snakes  of  North  America          .         .         .  569 

5.  The  Economic  Importance  of  Reptiles     ....  570 

6.  Prehistoric  Reptiles  .         .         .         .         .         .         -572 


CHAPTER  XX 

SuBPHYLUM  Vertebrata:  Class  VI.    Aves 

1.  The  Pigeon      .         .         .  ■       . 

2.  A  Brief  Classification  of  Birds  .... 

3.  A  Review  of  the  Orders  and  Families  of  Birds 

4.  A  General  Account  of  the  Class  Aves 

a,  Form  and  Function,  616;  b,  The  Colors  of  Birds, 
621  ;  c,  Bird  Songs,  621  ;  d,  Bird  Flight,  621  ;  e.  Bird 
Migration,  622 ;  f,  The  Nests,  Eggs,  and  Young  of 
Birds,  624;  g,  The  Economic  Importance  of  Birds, 
626 ;  h,  Domesticated  Birds,  630. 


575 
575 
588 

593 
616 


CONTENTS  xvii 


CHAPTER  XXI 

SuBPHYLUM  Vertebrata:  Class  VII.     Mammalia    .         .         .     632 

1.  The  Rabbit      .         « .633 

2.  A  Brief  Classification  of  Living  Mammals         .         .         .     641 

3.  A  Review  of  the  Principal  Orders  and  Families  of  Living 

Mammals  .         .         .         .'*■      .         .         .         .         .     645 

4.  General  Remarks  on  the  Mammalia  ....     676 

a,  Integumentary  Structures.  676 ;  b,  The  Teeth  of  Mam- 
mals, 678  ;  c,  The  Development  of  Mammals,  680 ; 
d,  Hibernation,  682 ;  e,  Migration,  683 ;  f,  Domesti- 
cated Mammals,  684 ;  g,  Fossil  Mammals,  685  ;  h,  The 
Economic  Importance  of  Mammals,  688. 

CHAPTER  XXII 

The  Ancestors  and  Interrelations  of  the  Vertebrates  691 

1.  The  Relations  between  Vertebrates  and  Invertebrates      .  691 

2.  The  Phylogenesis  of  Vertebrates 693 

3.  The  Fossil  Remains  of  Vertebrates 696 

a,  Succession  of  Life  in  General,  696;  b,  The  Evolu- 
tion of  the  Horse,  698. 


SCHEME  OF  THE  CLASSIFICATION  ADOPTED   IN 
THIS   BOOK 


Phylum  I.    PROTOZOA 27 


Class  I.  RHIZOPODA    .  . 

Order  i .  Lobosa  .     .  . 

"      2.  Heliozoa  .  . 

"      3.  Radiolaria  . 

"       4.    FORAMINIFERA 

Class  II.  MASTIGOPHORA 
Order  i.  Flagellata  . 
"     2.  Choanoflagel- 

LATA    .       .      .       . 

"  3.  Dinoflagellata 
"  4.  Cystoflagel- 

LATA    .       .       .       . 

Class  III.  SPOROZOA  .     .     . 
Subclass  I .  Telosporidia 


PAGE 
27 

39 

40 
40 
41 
41 
45 

47 
47 

48 
48 
52 


Order  i.  Gregarinida  .  52 

"        2.    COCCIDIIDEA      .  52 

"        3.    H^MOSPORIDIA  52 

Subclass  II.  Neosporidia  .     .  52 

Order  I.  Myxosporidia  52 

"     2.  Sarcosporidia  53 

Class  IV.  INFUSORIA  ...  53 

Subclass  I.  Ciliata      ...  62 

Order  i .  Holotricha     .  63 

"      2.  Heterotricha  63 

"     3.  Hypotricha     .  64 

"     4.  Peritricha      .  65 

Subclass  II.  Suctoria  ...  65 


Phylum  II.     PORIFERA 


Class  I.  CALCAREA      . 
Order  i.  Homoccela 


.  105  Class  III.  DEMOSPONGI^ 

.  105  Order  I.  Tetraxonida 

2.    HeTEROCCELA         .    105  "        2.    MONAXONIDA    . 

Class  II.  HEXACTINELLIDA    105  "      3.  Keratosa  .     . 


Phylum  III.     CCELENTERATA 


Class  I.  HYDROZOA 


Order 

I. 

Anthomedus^ 

128 

a 

2. 

Leptomedus^ 

128 

a 

3- 

Trachymedus^ 

128 

li 

4. 

NARCOMEDUSiE 

128 

u 

5- 

Hydrocoral- 

lin^   .     .     . 

.  129 

a 

6. 

^  Siphonophora 

.^129 

.  118    Class  II.  SCYPHOZOA.     . 
Order  i.  Stauromedus^ 

"  2.  PEROMEDUSiE  . 
"  3.  CUBOMEDUSiE  . 
"        4.    DISCOMEDUS.E 

Class  III.  ANTHOZOA  .     . 
Subclass  I .  Alcyonaria 
Order  i .  Stolonifera 


92 

105 
105 
105 
105 

108 

129 
132 
132 
133 
133 
133 
139 
139 


XX 


SCHEME   OF   THE   CLASSIFICATION 


PAGE 

Order  2.  Alcyonacea  .  139 

"  3.  Gorgon  ACE  A  .  139 

"  4.  Pennatulacea  140 

Subclass  11.  Zoantharia    .     .141 

Orderi.  Edwardsiidea    141 


PAGE 

Order 2.  Actiniaria  .  .  141 
"  3.  Madreporaria  141 
''  4.  zoanthidea  .  1 42 
"  5.  Antipathidea  .  142 
"      6.  Cerianthidea  .  142 


Phylum  IV.     CTENOPHORA 145 


Phylum  V.     PLATYHELMINTHES 


Class  I.     TURBELLARIA. 
Orderi.  Rhabdoccelida 
"     2.  Tricladida    . 
"      3.  Polycladida 


155  Class  II.  TR^MATODA 

156  Order  i.  Monogenea 

156  "      2.  Digenea     . 

157  Class  HI.  CESTODA     , 


150 

157 
161 
161 
163 


Phylum  VI.     NEMATHELMINTHES . 


.  169 


GROUPS  OF  INVERTEBRATES  OF  MORE  OR  LESS 


UNCERTAIN    SYSTEMATIC    POSITION 


Group  r.  Mesozoa  .     .     . 
''       2.  Nemertinea 
"       3.  Nematomorpha 
"      4,  Acanthocephala 
"      5.  Ch;etognatha  . 


176  Group  6.  Rotifera 

177  ''       7.  Bryozoa  .     . 

179  ''      8.  Phoronidea 

180  "      9.  Brachiopoda 
180  "     10.  Gephyrea     . 


.  176 

.  181 

.  183 
.  185 
.  185 

.  186 


Phylum  VII.     ECHINODERMATA 


[89 


Class  I.  ASTEROIDEA 
Class  11.  OPHIUROIDEA 
Class  III.  ECHINOIDEA 


.   198    Class  IV.  HOLOTHURIOIDEA  205 
.   199   Class  V.  CRINOIDEA    ...  208 

.  202 


Phylum  VHI.     ANNELIDA 


Class  I.  ARCHIANNELIDA    .  232 

Class  II.  CHiETOPODA     .     .  233 

Subclass  I.  Polychaeta     .     .  234 
Orderi.  Phaneroceph- 

ala      =     =     .  236 


Order  2.  Cryptoceph- 
ALA       .      . 
Subclass  II.  Oligochaeta  . 
Order  i.  Microdrilt 
"      2.  Macrodrili 
Class  III.  HIRUDINEA 


215 

236 
236 
236 
236 
236 


SCHEME   OF  THE   CLASSIFICATION 


XXI 


raxi^viyi 

PAGE 

i\V\Ji^\-.\J 

jy^r 

V. 

■i4ji 

Class  I.  AMPHINEURA     . 

251 

Order  2. 

PULMONATA 

258 

Order i .  Polyplaco- 

Class  III 

SCAPHOPODA  .     . 

261 

PHORA 

351 

Class  IV. 

PELECYPODA  .     . 

261 

-      2.  Aplacophora 

252 

«•  Order  i . 

Protobran- 

Class  II.  GASTROPODA    . 

252 

CHIA       .       . 

262 

Subclass  I.  Streptoneura 

258 

'a 

2. 

Filibranchia  . 

262 

Order  i.  Aspidobran- 

u 

3- 

Eulamelli- 

CHIA      .      . 

258 

branchia 

262 

"      2.  Pectinibran- 

a 

4- 

Septibranchia 

262 

CHIA       .       . 

.     258 

Class  V. 

CEPHALOPODA  .     . 

264 

Subclass  II.  Euthyneura . 

258 

Order  i . 

Tetrabran- 

Order  I.  Opisthobran- 

CHIA       . 

268 

CHIA      .      . 

.     258 

a 

2. 

Dibranchia 

268 

Phylum  X.     ARTHROPODA     .... 

274 

Class  I.  CRUSTACEA  .     . 

276 

Order  i . 

Pauropoda 

309 

Subclass  I.  Branchiopoda 

292 

u 

2. 

DiPLOPODA  .       . 

309 

Order  I.  Phyllopoda 

292 

u 

3- 

Chilopoda  .     . 

310 

"      2.  Cladocera 

294 

ii 

4- 

Symphyla   .     . 

311 

Subclass  II.  Ostracoda     . 

294 

Class  IV. 

INSECTA      .     .     . 

312 

•*        3.  Copepoda.     . 

294 

Order  i . 

Aptera  .     .     . 

337 

"        4.  Cirripedia 

294 

" 

2. 

Ephemerida    . 

338 

"         5.  Malacostraca 

294 

a 

3- 

Odonata     .     . 

339 

Order  i .  Nebaliacea 

294 

a 

4. 

Plecoptera     . 

340 

"      2.  Anaspidacea 

294 

a 

5- 

ISOPTERA        .       . 

340 

"      3.  Mysidacea  . 

294 

a 

6. 

CORRODENTIA    . 

341 

"     4.  Cumacea     . 

294 

u 

7. 

Mallophaga   . 

341 

"      5.  Tanaidacea 

297 

a 

8. 

Thysanoptera 

342 

"        6.    ISOPODA   .       . 

297 

u 

9- 

EUPLEXOPTERA 

342 

"     7.  Amphipoda 

297 

a 

10. 

Orthoptera    . 

343 

"     8.  Euphausiacea 

297 

a 

II. 

Hemiptera 

345 

"     9.  Decapoda   . 

297 

u 

12. 

Neuroptera    . 

349 

Suborder  i .  Natantia 

297 

u 

13- 

Mecoptera 

349 

"         2.  Reptantic 

I    297 

a 

14. 

Trichoptera  . 

350 

"    10.  Stomatopoda . 

297 

a 

15. 

Lepidoptera   . 

350 

Class  II.  ONYCHOPHORA 

305 

a 

16. 

Diptera  .     .     . 

356 

Class  III.  MYRIAPODA     . 

308 

a 

17- 

Siphonaptera 

359 

xxii  SCHEME   OF   THE   CLASSIFICATION 

PAGE  PAGE 

Order  i8.  Coleoptera     .  360  Order  5.  Pedipalpi    .     .  381 


''    19.  Hymenoptera 

364 

"      6. 

Palpigradi 

•    382 

Class  V.  ARACHNIDA 

371 

"      7- 

SOLIFUG^      . 

382 

Order  i .  Araneida    . 

371 

"      8. 

Chernetidia 

■    382 

"        2.    SCORPIONIDEA 

377 

"      9- 

Xiphosura  . 

383 

"     3.  Phalangidea 

379 

"    10. 

EURYPTERIDA 

•    384 

"     4.  Acarina 

379 

Phylum  XI.     CHORDATA      .     .     .  -  .     .386 

Subphylum  I.     ENTEROPNEUSTA 386 

Order  I.     Balanoglossida     .     .     ." •    .     .     .  386 

"      2.     Cephalodiscida 386 

Subphylum  IL     TUNICATA 389 

Order  i.     Ascidiacea 391 

"     2.     Thaliacea 393 

"      3.     Larvacea 393 

Subphylum  III.     CEPHALOCHORDA 393 

"  IV.     VERTEBRATA 400 

Class  I.     CYCLOSTOMATA 414 

Subclass  I.     Myxinoidea 420 

"         2.     Petromyzontia 420 

Class  II.     ELASMOBRANCHII .  422 

Subclass  I.     Selachii 428 

Order  i.     Squali        428 

"      2.     Raji 429 

Subclass  2.     Holocephali 430 

Class  III.     PISCES •  432 

Subclass  I.     Teleostomi 452 

Order  i.     Crossopterygii 452 

"      2.    Chondrostei 452 

"     3.    HoLOSTEi 454 

"     4.    Teleostei 455 

Subclass  2.     Dipnoi 471 

Class  IV.     AMPHIBIA 477 

Order  i.     Apoda 512 

"      2.     Caudata •     •     •  513 

"      3.     Salientia 517 


SCHEME  OF  THE   CLASSIFICATION  xxiii 

PAGE 

Class  V.     REPTILIA 527 

Order  1.     Testudinata 540 

"      2.     Rhynchocephalia 546 

"     3.     Crocodilini 547 

"     4.     Squamata 550 

Class  VI.     AVES '>■ 575 

Subclass  I.     Archaeornithes 593 

"         2.     Neornithes 594 

Order  i.     Hesperornithiformes 594 

"     2.    ichthyornithiformes 594 

"     3.    Struthioniformes    " 595 

"     4.    Rheiformes 596 

"     5.    Casuariiformes 596 

"     6.    Crypturiformes 596 

"        7.      DiNORNITHIFORMES 597 

"        8.      ^PYORNITHIFORMES 598 

"  9.  Apterygiformes 598 

"  10.  Sphenisciformes 598 

"  II.  Colymbiformes 599 

"  12.  Procellariiformes 600 

"      13.      CiCONIIFORMES 60I 

"    14.     Anseriformes 602 

"    15.     Falconiformes 603 

"    i'6.     Galliformes 606 

"    17.     Gruiformes 606 

"    18.     Charadriiformes 607 

"    19.    cuculiformik 610 

"    20,     coraciiformes 61o 

"    21.     Passeriformes 614 

Class  Vn.     MAMMALIA 632 

Subclass  I.     Prototheria 642 

Order  i.     Monotremata 645 

Subclass  II.     Eutheria 642 

Division  I.     DII>ELPHIA 642 

Order  I.     Marsupialia 647 

Division  H.     MONODELPHIA .642 

Section  A.     Ungidciilata 642 

Order  i.     Insectivora  .     ,     . 649 

"      2.     Dermoptera •  642 


XXIV 


SCHEME   OF   THE   CLASSIFICATION 


Order  3. 

a 

4- 

a 

5- 

a 

6. 

u 

7- 

a 

8. 

Chiroptera 650 

Carnivora 652 

rodentia 658 

Edentata 660 

Pholidota 661 

tubulidentata      .......  644 

Section  B.     Primates 644 

Order  9.    Primates 662 

Section  C.     Ungidata 644 

Order  10.     Artiodactyla 667 

"      II.     Perissodactyla 671 

"      12.     Proboscidea 672 

"        13.      SlRENlA 673 

"      14.    Hyracoidea 645 

Section  D.     Cetacea 645 

Order  15.     Odontoceti 674 

"      16.     Mystacoceti 675 


COLLEGE   ZOOLOGY 


COLLEGE   ZOOLOGY 

CHAPTER   I 
INTRODUCTION 

I.  General  Survey  or  the  Animal  Kingdom 

One  who  is  not  a  naturalist  or  who  does  not  have  access  to 
the  apparatus  necessary  for  the  examination  of  minute  objects 
usually  becomes  acquainted  with  only  a  few  of  the  many  kinds 
of  animals  that  inhabit  the  earth.  The  most  familiar  of  these 
are  the  comparatively  large  four-footed  beasts,  the  fish,  the 
frogs,  the  snakes,  the  birds,  and  the  insects.  The  majority  of 
animals  are  never  seen  by  most  people,  and  perhaps  never  even 
heard  of.  This  is  true  of  the  microscopic  parasite  which  is  pres- 
ent in  the  blood  of  malaria  patients,  of  the  coral  polyp  (Fig.  87) 
which  builds  up  entire  islands  in  the  sea,  of  the  Trichinella 
(Fig.  113),  a  parasitic  worm  which  sometimes  causes  a  human 
disease  called  trichinosis,  and  of  a  host  of  others. 

Scientists  have  found  it  convenient  to  separate  all  animals 
into  two  groups,  the  vertebrates  and  the  invertebrates.  The  ver- 
tebrates possess  a  backbone  or  vertebral  column  consisting  of  a 
linear  series  of  bones  called  vertebrae  (Fig.  418);  the  inverte- 
brates have  no  vertebral  column.  The  vertebrates  are  better 
known  than  the  invertebrates,  since  they  are  usually  large  and 
include  most  of  the  domesticated  animals.  The  invertebrates, 
however,  are  much  more  numerous  both  in  regard  to  the  number 
of  kinds  and  the  number  of  individuals.  Thus  of  the  eleven  main 
groups  (phyla)  of  animals  recognized  in  the  classification  adopted 
in  this  book  only  part  of  one  group,  the  Chord ata  (Chap.  XIV), 
deals  with  the  vertebrates,  whereas  the  rest  of  this  group  and 


2  COLLEGE  ZOOLOGY 

the  other  ten  chief  divisions  are  composed  entirely  of  inverte- 
brates. 

It  is  therefore  of  considerable  importance  at  the  very  beginning 
to  learn  something  of  the  characteristics  and  habitats  of  the 
thousands  of  living  creatures  that  form  the  basis  for  the  study  of 
zoology.  In  the  following  paragraphs  a  few  facts  about  each 
main  group  are  presented  in  such  a  way  as  to  give  a  bird's-eye 
view  of  the  entire  animal  kingdom. 

(i)  The  Vertebrates.  — The  members  of  this  group  possess  a 
bony  axis  of  vertebrae  called  the  vertebral  column  or  backbone 
(Fig.  418).  They  are  the  most  highly  developed  of  all  animals, 
and  include  man.  The  vertebrates  may  be  subdivided  into 
seven  assemblages,  each  containing  numbers  of  more  or  less 
familiar  forms. 

At  the  top  of  the  series  are  placed  the  Mammalia  (Chap. 
XXI),  usually  known  as  animals  or  beasts.  Among  the  repre- 
sentative mammals  are  man,  the  apes,  monkeys,  bats,  moles, 
rats,  mice,  rabbits,  dogs,  cats,  cows,  sheep,  horses,  whales,  sloths, 
opossums,  and  the  peculiar  duckbill  (Fig.  513)  and  spiny  ant- 
eater  of  Australia.  They  are  vertebrates  which  possess  hair, 
and,  with  a  few  exceptions,  nourish  their  young  with  milk  se- 
creted by  mammary  glands.  They  breathe  air  by  means  of 
lungs,  and  are  said  to  be  warm-blooded,  since  their  body  tem- 
perature is  nearly  100°  F.,  regardless  of  the  temperature  of  the 
surrounding  medium. 

The  members  of  the  group  Aves  or  Birds  (Chap.  XX)  are 
characterized  by  the  presence  of  feathers;  no  other  animals 
possess  these  structures.  Birds  are  air-breathers  and  warm- 
blooded, having  a  higher  body  temperature  than  any  other  or- 
ganisms. They  are  all  terrestrial,  though  many  of  them'  are 
adapted  to  life  on  or  near  the  water.  The  majority  of  the  birds 
are  able  to  fly  long  distances,  but  some  of  them,  like  the  ostrich 
and  the  auk,  are  flightless. 

Reptiles  (Chap.  XIX)  are  remarkably  diversified  in  form, 
and  occupy  many  kinds  of  habitats.     Most  of  them  live  on  land, 


INTRODUCTION  3 

but  the  turtles  and  alligators  spend  much  of  their  existence  in  the 
water;  the  lizards  are  in  many  cases  arboreal;  and  the  snakes 
live  in  almost  every  conceivable  environment.  They  -are  all 
called  cold-blooded  vertebrates  because  their  body  temperature 
varies  with  that  of  the  surrounding  medium  and  may  drop  to 
the  freezing  point.  They  possess  lungs,  and  in  most  cases  are 
covered  with  an  armor  of  scales  of  bony  plates. 

The  most  familiar  Amphibia  (Chap.  XVIII)  are  tho:  frogs,  toads, 
and  salamanders.  They  pass  the  first  part  of  their  lives  in  the 
water,  at  which  time  they  breathe  by  means  of  gills;  but  later 
they  become  air-breathers,  and  many  of  them  leave  the  water 
and  live  on  land.  In  form  certain  Amphibia  resemble  reptiles, 
but  they  usually  do  not  possess  scales  and  are  anatomically  quite 
different.     They  are  cold-blooded. 

The  common  fishes  are  members  of  the  group  Pisces  (Chap. 
XVII).  They  are  cold-blooded  animals,  usually  covered  with 
scales,  and  spend  their  entire  existence  in  the  water.  They  pos- 
sess gills  for  breathing,  and  swim  about  by  means  of  fins.  Some 
of  them,  like  the  sea-horse  (Fig.  398),  are  so  modified  as  to  be 
hardly  recognizable  as  fish;  others,  called  lung- fishes,  are  able 
to  breathe  out  of  water. 

Belonging  to  the  vertebrate  series,  but  lower  in  the  scale  of 
life  than  the  common  fishes,  are  two  groups  of  fishlike  animals 
that  are  comparatively  little  known.  These  are  the  Elasmo- 
BRANCHii,  or  sharks  and  rays  (Chap.  XVI),  and  the  Cyclosto- 
mata,  or  lamprey-eels  and  hagfishes  (Chap.  XV;  Fig.  352). 

(2)  The  Arthropoda. — The  crayfishes,  centipedes,  insects,  and 
spiders  are  among  the  commonest  Arthropoda  (Chap.  XIII). 
All  of  these  animals  have  jointed  appendages,  and  their  bodies 
are  divided  into  a  number  of  segments  which  are  arranged  in  a 
single  row  and  are  modified  for  various  purposes.  An  outer 
covering  of  a  yellowish  substance  called  chitin  gives  firmness  to 
the  body  and  also  serves  as  a  protection  from  mechanical  injury. 

The  Arachnida  are  the  spiders,  scorpions,  mites,  ticks,  etc. 
They  may  usually  be  distinguished  from  other  Arthropoda.  by 


4  COLLEGE  ZOOLOGY 

the  presence  of  eight  legs.  Many  of  them,  like  the  scorpion, 
are  capable  of  inflicting  severe  wounds  with  their  stings.  The 
curious  king-crab  is  now  placed  by  zoologists  in  the  group  Arach- 

NIDA. 

The  Insecta  are  the  butter  flies ,  bees,  beetles,  bugs,  etc.  They 
have  six  legs,  and  usually  possess  wings. 

The  Myriapoda  are  long,  slender,  terrestrial  animals  with 
one  or  two  pairs  of  legs  on  each  body  segment;  they  are  known  as 
centipedes  (Fig.  233)  and  millipedes  (Fig.  232). 

The  Crustacea  are  mainly  aquatic  Arthropoda,  and  breathe 
with  gills;  they  include  the  lobsters,  crayfishes,  crabs,  barnacles, 
sow  bugs,  and  many  others. 

(3)  The  Mollusca.  —  The  Mollusca  (Chap.  XII)  most  often 
seen  are  the  snails  and  clams;  the  slug,  oyster,  squid  (Fig.  191). 
nautilus  (Fig.  194),  cuttlefish,  and  octopus,  are  also  well  known. 
They  are  of  various  shapes  and  sizes,  but  most  of  them  possess  a 
ventral  muscular  structure  called  the  foot,  which  usually  serves 
as  an  organ  of  locomotion.  Often  a  heavy  shell  of  calcium  car- 
bonate covers  the  body. 

(4)  The  Annelida.  —  The  Annelida  (Chap.  XI)  are  known 
as  segmented  worms,  since  their  bodies  consist  of  sometimes  over 
one  hundred  rings  or  segments  and  their  shape  is  wormlike. 
The  earthworm  is  the  commonest  representative  of  the  group. 
There  are  many  marine  annelids,  and  also  a  number  of  fresh- 
water members,  Hke  the  leech.  The  medicinal  leech  (Fig.  169) 
is  famous  for  its  use  in  sucking  blood. 

(5)  The  Echinodermata.  —  The  starfish  (Fig.  131)  is  a  well- 
known  echinoderm,  and  usually  serves  as  a  type  of  the.  group. 
Like  all  echinoderms,  it  is  radially  symmetrical,  and  has  five  arms 
extending  out  from  a  central  disc.  The  other  echinoderms  are 
called  brittle  stars,  sea  urchins,  sea  cucumbers,  and  sea  lilies. 
Most  of  these  animals  have  a  body-^all  supplied  with  spicules 
of  calcium  carbonate;  hence  their  name,  which  means  spiny- 
skinned.  They  all  live  in  salt  water,  and  are  therefore  seldom 
seen  by  people  who  do  not  visit  the  sea  coast. 


,  INTRODUCTION  5 

(6)  The  Nemathelminthes.  —  The  Nemathelminthes  are 
unsegmented  round  or  thread  worms.  Most  of  them  are  parasitic 
like  the  roundworm,  Ascaris  (Fig.  iii),  which  inhabits  the 
alimentary  canal  of  man,  the  horse,  and  many  other  animals. 
One  dangerous  parasite  is  Trichinella  (Fig.  113),  which  spends 
part  of  its  life  in  the  muscle  of  thft  hog,  and  may  attack  human 
beings  if  infected  pork  is  eaten  without  being  sufficiently  cooked. 
Vinegar  usually  contains  a  number  of  roundworms  called  vinegar 
eels;  they  can  be  seen  only  with  the  aid  of  a  microscope. 

(7)  The  Platyhelminthes.  —  The  Platyhelminthes  or  flat- 
worms  are  also  worm-like  and  unsegmented.  The  best  known 
members  are  the  tapeworms,  which  are  parasitic  in  man  and  other 
animals.  The  liver  fluke  is  a  serious  pest;  it  inhabits  the  bile 
ducts  of  sheep  and  causes  the  death  of  large  numbers  of  infected 
individuals  in  certain  localities.  '  Less  widely  known  are  the  fresh- 
water flatworms,  like  Planaria  (Fig.  97),  and  the  terrestrial  and 
marine  forms. 

(8)  The  Ccelenterata.  —  The  Ccelenterata  are  mostly 
marine  animals,  and  are  known  as  hydroids  (Fig.  73)  and  jelly- 
fishes  (Fig.  82).  Their  bodies  are  fundamentally  simple  sacs, 
although  many  modifications  give  the  impression  of  great  com- 
plexity. Some  ccelenterates  are  famous  for  the  rigid  skeletal 
structures  they  produce;  this  is  true  of  the  coral  polyps  (Fig.  86), 
which  have  even  built  up  entire  islands.  There  are  only  a  few 
fresh- water  ccelenterates;  one  of  these,  Hydra  (Fig.  65),  is  com- 
paratively common,  and  is  studied  as  a  type  of  this  group  by 
most  students  of  biology. 

(9)  The  Porifera.  — The  Porifera  are  sponges.  The  ordinary 
bath  sponge  is  the  horny  skeleton  of  an  animal  that  lives  in  the 
sea  (Fig.  63).  Venus^s  flower  basket  (Fig.  62)  is  a  sponge  skele- 
ton that  is  often  seen  in  museums.  Most  of  the  sponges  secrete 
a  supporting  framework  of  calcium  carbonate  or  silica.  Only  a 
few  of  the  sponges  live  in  fresh  water,  and  none  lives  on  land. 

(10)  The  Protozoa.  —  The  Protozoa  (Chap.  II)  are  in  most 
cases  so  small  as  to  be  visible  only  with  the  microscope.     They 


6  COLLEGE  ZOOLOGY 

are,  however,  of  great  importance,  especially  those  which  cause 
diseases  such  as  malaria.  Protozoa  are  to  be  found  almost 
everywhere.  If  a  few  dead  leaves  are  placed  in  a  dish  of  water 
and  left  to  decay,  the  scum  which  forms  on  the  surface  will  be 
found  to  contain  thousands  of  these  minute  organisms.  The 
simplest  animals  belong  to  the  Protozoa;  among  these  are 
Ameba  (Fig.  9),  Paramecium  (Fig.  2)i),  and  Euglena  (Fig.  22), 
which  will  be  studied  in  some  detail  in  Chapter  II. 

Few  people  realize  the  abundance  and  variety  of  animal  life. 
Almost  every  part  of  the  earth  is  inhabited  by  animals  of  some 
kind,  and  these  animals  are  more  or  less  restricted  to  certain 
kinds  of  habitats.  For  example,  fishes  live  in  the  water,  earth- 
worms in  the  ground,  the  polar  bear  in  Arctic  regions,  the  ele- 
phant in  the  Tropics,  the  prairie  dog  on  the  prairies,  the  moun- 
tain goat  on  the  mountains,  and  parasites  upon  or  within  the 
bodies  of  other  organisms.  Four  principal  kinds  of  animals 
may  be  recognized  according  to  their  mode  of  existence:  (i)  ma- 
rine animals  living  in  the  salt  waters  of  the  sea,  (2)  fresh-water 
animals  living  in  fresh-water  streams,  ponds,  and  lakes,  (3)  ter- 
restrial animals  living  on  land,  and  (4)  parasites  which  live  on  or 
within  the  bodies  of  other  animals. 

The  oceans  are  inhabited  by  millions  of  animals  of  all  sizes, 
ranging  from  the  whale  to  the  microscopic  floating  organisms 
known  as  plankton.  Salt-water  animals  are  restricted  to  certain 
definite  regions;  some  float  on  or  near  the  surface,  and  others 
live  at  various  distances  from  the  surface,  until  a  depth  is  reached 
where  the  light  never  penetrates.  As  a  rule,  animals  living  in 
salt  water  die  almost  at  once  if  transferred  to  fresh  water;  like- 
wise salt  water  is  fatal  to  fresh-water  animals. 

Every  pond,  lake,  brook,  creek,  and  river  is  inhabited  by  a  host 
of  living  animals.  A  pond,  for  example,  furnishes  a  home  for 
the  early  stages  in  the  life  history  of  the  mosquito,  whose  eggs  are 
laid  in  a  raft-like  mass  on  top  of  the  water,  and  whose  young 
swim  about  at  or  near  the  surface.  Frogs  and  salamanders  find 
a  home  amid   the  vegetation   common  to  ponds.     Crayfishes 


INTRODUCTION  7 

crawl  about  on  the  bottom;  wheel  animalcules  (Fig.  122)  and 
many  other  extremely  small  animals  swim  about  in  search  of 
food;  and  almost  every  drop  of  pond  water  contains  a  number 
of  microscopic  forms. 

The  terrestrial  animals  are  the  ones  best  known  to  the  average 
person,  and  every  one  is  aware  c^f  the  vast  numbers  of  deer, 
wolves,  field-mice,  snakes,  insects,  and  other  forms  that  move 
about  on  the  surface  of  the  earth.  Animals  like  the  mole  and  the 
earthworm  which  live  underground  are  said  to  be  subterrestrtal, 
and  those  like  the  birds  and  butterflies  that  frequent  the  air  are 
called  aerial. 

Parasites  are  more  widely  spread  than  is  generally  known. 
Almost  every  animal  is  infested  with  others  which  prey  upon  it. 
The  malarial  fever  germ  is  one  of  the  most  important,  although 
one  of  the  smallest,  parasites.  The  fleas  and  lice  are  called 
external  parasites.  The  internal  parasites  of  man  include  the 
roundworm  Ascaris  (Fig.  in),  the  tapeworm  (Fig.  107),  and 
the  Trichinella  (Fig.  113).  Frequently  parasites  are  preyed  upon 
by  other  parasites,  —  a  condition  known  as  hyperparasitism  — 
and  even  the  hyperparasites  may  be  parasitized.  Thus  the  fol- 
lowing humorous  lines  contain  a  grain  of  truth:  — 
"  Great  fleas  have  little  fleas 

Upon  their  backs  to  bite  'em, 

And  little  fleas  have  lesser  fleas. 

And  so  ad  infinitum y 

The  survey  of  the  animal  kingdom  just  concluded  attempts  to 
present  a  few  facts  about  the  groups  of  animals  to  be  studied  in 
the  succeeding  chapters.  The  most  highly  organized  and  most 
familiar  animals,  the  mammals^  were  considered  first,  and  the 
less  complex  were  successively  discussed  in  a  descending  series, 
until  the  last  and  simplest  organisms  were  reached.  A  glance  at 
the  table  of  contents  of  this  book  will  show  that  the  extended 
studies  of  these  groups  have  been  arranged  in  a  reversed  order, 
beginning  with  the  simplest  animals,  the  Protozoa,  and  ending 
with  the  highest  type,  the  Mammal.     This  method  of  presenting 


8  COLLEGE  ZOOLOGY 

the  facts  of  zoology  has  been  employed  with  the  idea  of  organic 
evolution  in  mind. 

Practically  every  zoologist  at  the  present  time  believes  that 
the  complex  animals  have  evolved  from  simpler  forms  at  some 
period  in  the  world's  "history.  How  this  evolution  has  taken 
place  is  still  a  moot  question.  According  to  the  evolution  theory 
the  first  animals  that  existed  on  the  earth  consisted  of  a  single 
cell,  and  all  the  animals  that  lived  at  that  time  would  now  be 
called  Protozoa  (Chap.  II).  These  animals  gave  rise  in  some 
way  still  unknown  to  organisms  consisting  of  many  cells  (Chap. 
III).  In  the  course  of  millions  of  years  new  and  more  complex 
forms  were  continually  being  evolved  from  older  and  simpler 
animals,  so  that  all  those  now  existing  may  be  arranged  in  an 
ascending  series  constituting  a  sort  of  genealogical  tree.  Many 
of  the  connecting  links  between  the  various  groups  have  disap- 
peared, but  in  a  few  cases  the  remains  preserved  in  the  rocks  as 
fossils  give  us  very  definite  ideas  of  the  order  of  evolution. 

Man  is  no  exception  in  the  evolutionary  process,  but  is  closely 
allied  to  the  anthropoid  apes,  and  doubtless  arose  from  an  ape- 
like ancestor.  The  simpler  animals  living  to-day  probably  do 
not  represent  ancestral  forms,  since  they  have  become  modified 
in  many  ways.  It  is  only  safe  to  make  general  statements,  such 
as,  that  man  has  evolved  from  ape-like  ancestors,  that  the  birds 
have  arisen  from  reptile-like  ancestors,  and  that  the  insects 
have  descended  from  worm-like  ancestors. 

(^2r)LiviNG  Matter  contrasted  with    Non-living  Matter 

All  living  things  are  either  plants  or  animals,  and  have  certain 
peculiarities  which  separate  them  from  non-living  things.  These 
peculiarities  do  not  all  pertain  exclusively  to  living  organisms, 
but  may,  to  a  certain  extent,  be  attributes  of  non-living  bodies; 
nevertheless,  when  taken  together,  they  are  sufficient  to  deter- 
mine whether  an  object  is  living  or  lifeless.  The  most  important 
peculiarities  are  as  follows:  — 


INTRODUCTION 


(i)  Definite  Size.  —  The  size  of  living  organisms  varies  within 
definite  limits.  The  smallest  animals  known  are  microscopic 
blood  parasites;  the  largest  living  animals  are  the  whales.  The 
difference  is  great  but  definite,  and  eacj^  kind  of  animal  has  a 
characteristic  size.  Non-living  bodies,  on  the  other  hand,  may 
be  of  any  size;  for  example,  wat?er  may  exist  as  a  particle  of 
vapor  or  as  an  ocean. 

(2)  Definite  Form.  —  If  animals  were  not  constant  in  form,  we 
would  be  unable  to  distinguish  one  from  another.  Non-living 
bodies  usually  have  no  definite  form,  but  may,  like  water  in  a 
lake-bed,  assume  the  shape  temporarily  forced  upon  them. 

(3)  Definite  Chemical  Composition.  —  The  elements  found  in 
living  matter  are  all  found  in  non-living  bodies,  but  in  living 
matter  certain  elements  are  combined  so  as  to  produce  a  sub- 
stance known  as  protoplasm.  These  elements  are  present  in  a 
typical  animal  in  the  following  proportions:  — 

Carbon 


Oxygen 
Nitrogen 
Hydrogen 
Sulphur 

Phosphorus 

Chlorine 

Potassium 

Sodium 

Magnesium 

Calcium 

Iron 


99  per  cent  of  weight; 


I  per  cent  of  weight. 


(4)  Definite  Organization.  —  The  protoplasm  contained  in 
the  bodies  of  animals  is  not  continuous  in  most  cases  but  is 
divided  up  into  small  units  called  cells  (p.  13,  Fig.  2).  A  cell  is 
a  small  mass  of  protoplasm  containing  a  nucleus.  The  bodies 
of  some  animals  are  composed  of  only  a  single  cell  (Protozoa, 
Chap.  II),  but  all  of  the  more  highly  organized' animals  are  made 


lO  COLLEGE  ZOOLOGY 

up  of  almost  countless  numbers.  Non-living  bodies  possess  no 
unit  of  structure  comparable  to  the  cell. 
/  (5)  Metabolism.  —  Animals  are  able  to  change  food  into 
protoplasm;  this  process  is  termed  metabolism _(v.  19);  growth 
takes  place  by  the  addition  of  these  particles  of  protoplasm 
among  the  preexisting  particles.  This  is  growth  by  intussuscep- 
tion. Non-living  bodies  are  not  metaboHc,  and,  if  they  can  be 
said  to  grow  at  all,  increase  in  size  by  the  addition  of  particles 
on  the  outside,  that  is,  growth  is  by  accretion. 

(6)  Reproduction.  —  Animals  are  able  to  produce  other  ani- 
mals like  themselves.  Non-living  bodies  cannot  reproduce  their 
kind. 

(7)  Irritability  or  Reactiveness.  —  Animals  have  the  ability 
of  responding  to  changes  in  their  environment.  The  change  is 
termed  a  stimulus,  and  the  sum  total  of  the  animal's  movements 
is  known  as  its  behavior.     Non-living  ob'ects  are  not  irritable. 

3.  The  Physical  Basis  of  Life  —  Protoplasm 

Protoplasm  is  a  term  used  by  both  zoologists  and  botanists  to 
designate  the  essential  substance  of  which  plants  and  animals 
are  composed.  All  living  organisms  are  built  up  of  protoplasm, 
but  no  non-living  object  possesses  any  of  this  compound.  Pro- 
toplasm has  been  called  by  Huxley  "  the  physical  basis  of  life," 
since  all  vital  phenomena  are  due  to  its  presence. 

There  are  several  theories  regarding  its  structure:  A,  the 
alveolar  theory,  B,  the  reticular  theory,  and  C,  the  granular 
theory.  According  to  the  alveolar  theory  (Fig.  i)^  protoplasm 
consists  of  two  substances,  one  of  which  is  in  the  shape  of 
spheres  embedded  in  the  other.  The  reticular  theory  (B)  con- 
siders protoplasm  a  network  of  Pving  anastomosing  fibers 
among  which  are  non-living  substances  such  as  water  and  fat. 
The  third  theory  (C)  maintains  that  protoplasm  is  composed 
of  innumerable  living  granules  variously  arranged.  It  is  still 
uncertain  which  of  these  theories,  if  any^  is  correct. 


INTRODUCTION 


\T 


Ninety-seven  per  cent  of  protoplasm  consists  of  the  following 
four  elements :  — 

Oxygen 65.0  per  cent 

Carbon 18.5  per  cent 

Hydrogen \     .     .     .  ii.o  per  cent 

Nitrogen 2.5  per  cent 

These  and  other  elements  form  rather  definite  compounds. 
The  principal  inorganic  constituents  of  protoplasm  are  (i)  water, 
which  comprises  more  than  50  per 
cent  of  the  weight  of  most  animals, 
(2)  salts,  such  as  the  chlorides,  car- 
bonates, and  phosphates,  and  (3)  gases, 
such  as  oxygen  and  carbon  dioxide. 

The  organic  compounds  found  in  pro- 
toplasm comprise  the  proteids,  carbo- 
hydrates, and  fats.  Proteids  consist  of 
large  molecules  which  always  contain 
carbon,  oxygen,  hydrogen,  and  nitro- 
gen. They  do  not  dissolve  in  water, 
but  absorb  quantities  of  this  fluid, 
swelling  up  like  a  sponge.  Other 
peculiarities  are  their  inability  to  pass 
through  animal  membranes  and  their 
property  of  coagulation  or  clotting. 
Carbohydrates  are  compounds  of  car- 
bon, hydrogen,  and  oxygen,  the  last  two 
nearly  always  occurring  in  the  same 

,  .  ,      ,  .  -  .  Fig.    I.  —  Alveolar     struc- 

proportion  m  which  they  are  found  m   ture  of  the  protoplasm  of  an 
water  (H2O).    Starches  and  sugars  are  epidermis  cell  of    an  earth- 

,     -      ,  _  ...         worm.     (From  Verworn,  after 

common  carbohydrates.     Some  livmg   Butschli.) 

substances  apparently  do  not  contain 

this  compound.     Fats  are  likewise  not  invariable  constituents  of 

protoplasm.   The  protoplasm  of  each  species  of  animal  differs  from 

that  of  every  other  species,  but  in  all  it  has  similar  characteristics. 


12  COLLEGE  ZOOLOGY 

4.  The  Origin  of  Life 

No  one  knows  when  and  where  life  originated  on  the  earth. 
Many  of  the  ancients  believed  that  animals  were  created  by 
divine  providence,  but  this  theory  of  special  creation  is  not 
accepted  by  present-day  zoologists.  Historically  the  special  cre- 
ation theory  was  followed  by  that  of  spontaneous  generation.  Ac- 
cording to  this  theory  animals  were  supposed  to  originate  directly 
from  inorganic  substances;  for  example,  frogs  and  toads  from 
the  muddy  bottom  of  ponds  under  the  influence  of  the  sun,  and 
insects  from  dew.  The  brilliant  experiments  of  Redi  (1668), 
Pasteur  (1864),  and  Tyndall  (1876)  overthrew  this  theory  com- 

Cpletely,  and  scientists  now  believe  that  living  organisms  originate 
only  from  preexisting  organisms.  Where  life  first  began  is  still 
tmknown,  but  the  meeting  point  of  sea  and  land  is  the  most 
probable  place  of  origin.  From  here  the  fresh  water,  deep  sea, 
and  land  were  gradually  peopled. 

5.  The  Cell  and  the  Cell  Theory 

(i)  Structure.  —  It  has  already  been  noted  that  the  body  of  an 
animal  is  divided  up  into  microscopic  units  called  cells,  and  that 
each  cell  is  a  small  mass  of  protoplasm  containing  a  nucleus.  Cells 
vary  in  size  and  form;  some  are  extremely  small,  e.g.  blood 
parasites,  whereas  others,  like. the  egg  of-  a  bird,  are  very  large. 
They  have  no  definite  shape,  but  may  be  columnar,  flat,  spher- 
ical, or  long  and  thin  (Fig.  46).  The  number  of  cells  in  a  com- 
plex animal  is  enormous;  there  are  about  9,200,000,000  in  the 
gray  matter  of  the  human  brain.  ,0n  the  other  hand,  certain 
animals  (Protozoa)  consist  of  but  a  single  cell.  The  size  of  the 
animal  does  not  depend  upon  the  size  of  its  cells,  but  upon  their 
number. 

Figure  2  shows  the  essential  structure  of  a  cell.  The  largest 
part  of  the  contents  is  the  cytoplasm.  Within  this  substance  is 
embedded  a  nucleus.  At  certain  stages  in  the  life  activities  of 
the  cell  an  attraction-sphere  enclosing  one  or  two  c'entrosomes  is 

i 


INTRODUCTION 


13 


visible.  Vacuoles,  plastids,  and  non-living  bodies  (metaplasm) 
may  also  be  present.  The  entire  cell  may  or  may  not  be  sur- 
rounded by  a  membrane. 

The  cell  nucleus  contains  a  fluid  through  which  runs  a  network 
of  thin  linin  fibers.     Scattered  about  on  these  fibers  are  granules 


Attraction-sphere  encloajpg  two  centrosomes 


Plastids  lying 
in  the  cyto- 
plasm 


Chromatin- 

network 

Linin-net- 

work 


Karyosome, 
net-knot,  or 
chromatin- 
nucleolus 


•  Vacuole 


Fig.  2.  —  Diagram  of  a  cell.     (From  Wilson.) 


■  Passive  bodies 
(metaplasm  or 
paraplasm) 
suspended  in 
the  cyto- 
plasmic mesh- 
work 


of  chromatin y  a  substance  that  has  a  strong  affinity  for  certain 
dyes.  Frequently  several  granules  of  chromatin  unite  to  form 
a  net-knot  or  karyosome.  In  addition  to  these  regular  constit- 
uents of  the  nucleus,  one  or  more  bodies,  known  as  nucleoli,  may 
be  present.  In  certain  cases  a  cell  may  possess  more  than  one 
nucleus,  and  a  few  cells  have  no  definite  nucleus,  but  contain 
chromatin  granules  which  are  scattered  about  in  the  cytoplasm. 
(2)  Physiology.  —  There  is  a  definite  division  of  labor  among 
the  parts  of  a  cell.     The  particular  function  of  the  nucleus,  aside 


14 


COLLEGE  ZOOLOGY 


from  its  important  relation  to  cell  division,  to  be  described  later, 
seems  to  be  the  control  of  the  activities  by  which  the  protoplasm 
is  elaborated. 

The  cytoplasm,  from  its  direct  relation  to  the  outside  world, 
is  the  seat  of  such  functions  as  irritability,  absorption,  digestion, 
excretion,  and  respiration.  The  centrosome  is  of  importance 
during  cell  division.  The  cell  covering  may  serve  for  pro- 
tection or  support,  or  may  be  extremely  delicate  and  have  sig- 
nificance only  as  it  helps  to  control  the  absorption  of  certain 
fluids.  Plastids  may  represent  stored  food  or  waste  products; 
some  of  them,  however,  have  other  functions,  e.g.  the  chloro- 
plasts,  which  carry  on  photosynthesis  in  many  plants  and  a  few 
animal  cells. 

(3)  Cell  Division.  —  Cells  multiply  either  by  direct  division 
(amitosis)  or  indirect  division  (mitosis) .     In  amitosis  (Fig.  1 1) 


Fig.  3. — Amitosis.     Amitotic  nuclear  division  in  the  follicle  cells  of  a 
cricket's  egg.     (From  Dahlgren  and  Kepner.) 

the  nucleus  is  either  pinched  in  two  in  the  middle,  or  a 
plate  is  formed  in  the  plane  of  division,  which  later  be- 
comes double,  and  then  the  two  plates  separate,  or  two  nuclear 
membranes  are  built  up  inside  of  the  old  membrane.  The  cell 
body  then  divides,  though  in  many  cases  this  process  does  not 
occur  (Fig.  3).     Amitosis  is  characteristic  of  senescent  cells. 

Mitosis  is  the  usual  method  of  nuclear  division.  It  consists 
of  a  series  of  complex  processes  that  may  be  arranged  into 
four  phases.  Constant  reference  to  Figure  4  will  make  clear  the 
following  brief  account. 

{a)  During  the  prophase  the  chromatin  granules  that  are  scat- 
tered through  the  nucleus  in  the  resting  cell  (A)  become  ar- 


INTRODUCTION 


15 


ranged  in  the  form  of  a  long  thread  or  spireme  (B).  At  the  same 
time  the  centrosomes  move  apart  (A,  c ;  B,  a).  The  radiating 
lines  that  appear  about  them  (B)  later  give  rise  to  a  spindle  (C). 

A  B 


Fig.  4.  —  Mitosis.  Diagrams  illustrating  mitotic  cell  division.  (From 
Wilson.)  A,  resting  cell;  B,  prophase  showing  spireme  and  nucleolus  within 
the  nucleus  and  the  formation  of  spindle  and  asters  (a);  C,  later  prophase  show- 
ing disintegration  of  nuclear  membrane,  and  breaking  up  of  spireme  into 
chromosomes;  D,  end  of  prophases,  showing  complete  spindle  and  asters  with 
chromosomes  in  equatorial  plate  (ep);  E,  metaphase  —  each  chromosome  splits 
in  two;  F,  anaphase  —  the  chromosomes  are  drawn  toward  the  asters,  if  = 
interzonal  fibers;  G,  telophase,  showing  reconstruction  of  nuclei;  H,  later 
telophase,  showing  division  of  the  cell  into  two.    . 

While  this  is  going  on  the  nuclear  membrane  generally  disin- 
tegrates and  the  spireme  segments  into  a  number  of  bodies  called 
chromosomes  (C);  these  take  a  position  at  the  equator  of  the 
spindle,  halfway  between  the  centrosomes  (D,  ep).  The  stage 
shown  in  Figure  4,  D,  is  known  as  the  amphiaster;  at  this  time 


l6  COLLEGE  ZOOLOGY 

all  of  the  machinery  concerned  in  mitosis  is  present.  There  are 
two  asters  J  each  consisting  of  a  centrosome  surrounded  by  a  num- 
ber of  radiating  astral  rays,  and  a  spindle  which  lies  between 
them.     The  chromosomes  lie  in  the  equatorial  plate  {ep). 

(b)  During  the  second  stage,  the  metaphase,  the  chromosomes 
split  in  such  a  way  that  each  of  thdr  parts  contains  an  equal 
amount  of  chromatin  (E,  ep).  As  we  shall  see  later,  this  is  one 
of  the  most  significant  events  that  takes  place  during  mitosis. 

(c)  During  the  anaphase  (F)  the  chromosomes  formed  by  split- 
ting move  along  the  spindle  fibers  to  the  centrosomes.  As  a 
result  every  chromosome  present  at  the  end  of  the  prophase  (D) 
sends  half  of  its  chromatin  to  either  end  of  the  spindle.  The 
mechanism  that  brings  about  this  migration  is  as  yet  somewhat 
in  question.  Fibers  are  usually  left  between  the  separating 
chromosomes;^  these  are  known  as  interzonal  fibers  (F,  if). 

(d)  The  telophase  (G,  H)  is  a  stage  of  reconstruction  from  which 
the  nuclei  emerge  in  a  resting  condition;  the  chromatin  becomes 
scattered  throughout  the  nucleus,  which  is  again  enveloped  by 
a  definite  membrane  (H) ;  the  centrosome  divides  and,  with  the 
centrosphere,  tal^s  a  position  near  the  nucleus.  Finally  the 
cycle  is  completed  by  the  constriction  of  the  cell  into  two  daugh- 
ter cells. 

Chromosomes.  —  Every  species  of  animal  has  a  definite 
number  of  chromosomes  that  appear  when  the  cells  of  its 
body  undergo  mitosis.  Thus  sixteen  are  characteristic  of 
the  cells  of  oxen,  guinea  pigs,  and  inan;  the  grasshopper  has 
twelve;  and  the  brine  shrimp  (Artemia)  one  hundred  and  sixty- 
eight.  An  even  number  of  chromosomes  is  characteristic  of 
most  animals,  but  recent  researches  have  demonstrated  that 
some  forms,  particularly  the  males  of  insects,  have  an  odd 
number.  The  chromosomes  are  considered  by  most  zoologists 
to  be  the  bearers  of  hereditary  qualities  from  parent  to 
offspring. 

In  concluding  this  account  of  cell  division  two  points  are 
worthy  of  special  emphasis.     First,  with  regard  to  the  continuity 


INTRODUCTION 


17 


of  the  chromatin,  it  may  be  said  that  the  chromatin  is  continuous 
from  one  cell  generation  to  another.  The  cells  resulting  from 
mitosis  may  differ  greatly  in  size,  but  the  chromatin  seems  to 
be  divided  equally  between  them  with  great  exactness.  Second, 
cells  are  never  known  to  arise  except  from  preexisting  cells.  These 
two  facts  are  perhaps  the  most  important  for  us  to  keep  in  mind 
as  we  go  on  to  study  the  more  complex  problems  of  fertilization 
and  cell  division  in  the  many-celled  animals. 

(4)  The  Cell  Theory.  —  Cells  were  first  described  by  Hooke, 
an  Englishman,  in  1665.    The  regular  arrangement  of  the  com- 


:-»« 


Fig.  S- 


Cells  of  cork.     Facsimile  of  a  figure  by  Hooke.     (From  Farmer 
in  Lankester's  Zoology.) 


partments  in  cork  (Fig.  5)  reminded  him  of  the  cells  of  the  monks 
in  a  monastery  and  suggested  the  term.  In  1833  Brown  de- 
scribed the  nucleus  as  a  constant  cell  element,  and  a  few  years 
later  Schleiden  (1838)  and  Schwann  (1839)  advanced  the  idea 
that  all  plants  and  animals  are  composed  of  cells.  For  many 
years  the  cell-wall  was  considered  the  important  part  of  the 
structure,  but  later  the  protoplasm  within  it  was  recognized  as 
the  principal  constituent,  and  the  cell  was  then  defined  as  a 
mass  of  protoplasm  containing  a  nucleus  (Max  Schultze,  1861). 
The  importance  attached  to  the  cell  theory  may  be  judged 


l8  COLLEGE  ZOOLOGY 

from  the  following  quotation  from  E.  B.  Wilson,  the  foremost 
investigator  of  cellular  phenomena  in  this  country. 

"  During  the  half-century  that  has  elapsed  since  the  enuncia- 
tion of  the  cell-theory  by  Schleiden  and  Schwann,  in  1838-1839, 
it  has  become  ever  more  clearly  apparent  that  the  key  to  all 
ultimate  biological  problems  must,  in  the  last  analysis,  be  sought 
in  the  cell.  It  was  the  cell-theory  that  first  brought  the  struc- 
ture of  plants  and  animals  under  one  point  of  view,  by  revealing 
their  common  plan  of  organization.  It  was  through  the  cell- 
theory  that  Kolliker,  Remak,  NageH,  and  Hofmeister  opened 
the  way  to  an  understanding  of  the  nature  of  embryological  de- 
velopment, and  the  law  of  genetic  continuity  lying  at  the  basis 
of  inheritance.  It  was  the  cell-theory  again  which,  in  the  hands 
of  Goodsir,  Virchow,  and  Max  Schultze,  inaugurated  a  new  era 
in  the  history  of  physiology  and  pathology,  by  showing  that  all 
the  various  functions  of  the  body  in  health  and  in  disease  are 
but  the  outward  expressions  of  cell  activities.  And  at  a  still 
later  day  it  was  through  the  cell-theory  that  Hertwig,  Fol,  Van 
Beneden,  and  Strasburger  solved  the  long-standing  riddle  of 
the  fertilization  of  the  egg  and  the  mechanism  of  hereditary 
transmission.  No  other  biological  ge/^eraiization,  save  only  the 
theory  of  organic  evolution,  has  brought  so  many  apparently 
diverse  phenomena  under  a  common  point  of  view,  or  has  accom- 
plished more  for  the  unification  of  knowledge.  The  cell-theory 
must  therefore  be  placed  beside  the  evolution-theory  as  one  of  the 
foundation  stones  of  modern  biology." 

6.   Plants  contrasted  with  Animals 

It  is  easy  to  choose  characteristics  that  will  serve  to  distinguish 
a  tree  from  a  man,  but  the  separation  of  the  simplest  animals 
from  the  simplest  plants  is  a  more  difficult  problem.  In  fact, 
there  are  at  the  present  time  a  number  of  organisms  that  are 
claimed  by  both  botanists  and  zoologists.  There  is  no  single 
peculiarity  which  can  be  used  in  all  cases  to  discriminate  between 


INTRODUCTION 


19 


these  groups  of  organisms.  The  view  now  generally  accepted 
is  that  plants  and  animals  originated  together  but  have  devel- 
oped along  divergent  lines.  However,  certain  general  features 
can  be  indicated  in  which  the  two  kingdoms  differ.  These  are 
given  in  Table  I;  but  the  reader  should  bear  in  mind  that  there 
are  exceptions  to  every  one  of  these  criteria. 

TABLE  I 


THE  CHARACTERISTICS   OF  PLANTS  CONTRASTED  WITH  THOSE   OF 
ANIMALS 


1.  Structure 

2.  Locomotion 

3.  Irritability 


Plants 
Form    of    body    rather 
variable ;  new  organs 
added  externally. 

Usually  none  in  adult 

condition. 
Respond      to      stimuli 

slowly ;     no    nervous 

system. 


4.  Metabolism  Possess        chlorophyll ; 

manufacture  organic 
food  from  CO2  and 
H2O  in  the  presence 
of  light. 

5.  Waste  products    Oxygen,  carbon  dioxide, 

water. 


Animals 

Form  of  body  usually 
invariable ;  organs 
compact  and  mostly 
internal. 

Usually  well  developed. 

Respond  to  stimuli 
quickly ;  nervous 
system  present  in 
higher  forms. 

No  chlorophyll ;  re- 
quire organic  food. 


Carbon  dioxide,  water, 
urea,  faeces. 


One  of  the  principal  differences  between  plants  and  animals 
is  in  their  method  of  obtaining  food  and  changing  it  into  proto- 
plasm. The  processes  involved  are  included  under  the  term 
metaoolism.  Those  processes  which  use  energy  to  build  up  com- 
pounds are  said  to  be  anabolic;-  those  which  destroy  substances 
to  produce  energy  are  katabolic.    Animal?.,  as  shown  in  Figure  6, 


20  COLLEGE  ZOOLOGY 

take  in  food  which  is  digested  and  assimilated,  that  is,  dissolved, 
absorbed,  and  changed  into  protoplasm.  Oxygen  is  also  taken 
in  during  respiration;    this  unites  with  protoplasm  (oxidation), 


Fig.  6.  —  Metabolism.     Diagram  showing  the  various  metabolic 
activities  of  animals. 

furnishing  energy  and  producing  waste  products  or  excretions. 
Animals  are  primarily  katabolic  organisms,  being  unable  to 
manufacture  organic  compounds  from  simple  inorganic  substances. 


CARBON  DIOXIDE 


Fig.  7.  —  Metabolism.     Diagram  showing  the  manufacture  of  food 
by  plants  (photosynthesis). 

Plants  or  other  animals  are  therefore  absolutely  necessary  for 
their  existence. 

Plants,  on  the  other  hand,  are  able  to  manufacture  food  from 
inorganic. matter  by  a  process  known  as  photosynthesis  (Fig.  7). 


INTRODUCTION  21 

Carbon  dioxide  and  water  are  taken  into  the  plant  and  are 
changed  into  starch  by  means  of  a  green  substance  known  as 
chlorophyll.  Light  is  necessary  for  this  process.  A  by-product 
of  photosynthesis  is  oxygen. 

The  qualities  that  are  usually  cited  as  being  peculiarly  char- 
acteristic of  animals  are  locomotion-  and  nervous  activity.  With 
the  exception  of  a  few  extremely  sensitive  species  of  which  the 
common  sensitive  plant,  Mimosa  pudica,  is  the  most  familiar 
example,  plants  respond  very  slowly  to  external  stimuli,  and  their 
power  of  transmitting  impulses  is  poorly  developed.  Locomo- 
tion is  impossible  except  in  a  few  simple  forms  and  free  swimming 
reproductive  cells. 

7.  Classification 

It  is  natural  when  a  large  number  of  dissimilar  objects  are 
collected  to  attempt  to  place  them  in  groups  according  to  the 
presence  or  absence  of  certain  characteristics.  This  is  known  as 
classification.  Animals  are  not  infinitely  variable,  since  only 
about  five  hundred  thousand  species  have  been  described,  and 
they  may  be  classified  in  several  ways. 

By  artificial  classification  we  mean  the  grouping  of  animals 
according  to  some  resemblance  in  structure,  color,  habitat,  etc. 
For  example,  certain  animals  may  be  said  to  be  aquatic  because 
they  live  in  the  water;  others  terrestrial,  because  they  live  on 
land.  Or  certain  animals  are  said  to  be  carnivorous  because  they 
eat  flesh,  others  herbivorous  because  they  live  on  vegetable  food, 
and  still  others  omnivorous  because  they  devour  both  animal 
and  vegetable  matter. 

It  is  often  convenient  to  use  an  artificial  classification,  but 
for  all  scientific  work  the  natural  classification  is  employed. 
This  is  an  attempt  to  seek  out  the  relationships  of  animals  and 
to  group  them,  not  because  of  superficial  resemblances,  but  on 
a  basis  of  their  similarity  in  structure  and  probable  kinship.  A 
number  of  large  divisions,  known  as  phyla,  are  recognized  by 
zoologists.     Each  phylum  is  again  divided  into  classes,  each 


22  COLLEGE  ZOOLOGY 

class  into  orders,  each  order  into  families,  each  family  into 
GENERA,  and  each  genus  into  species. 

The  gray  wolf,  for  example,  belongs  to  the  species  occidentalis 
of  the  genus  Cams.  This  genus,  along  with  others,  such  as  the 
genus  Vulpes,  which  contains  the  red  fox,  constitute  the  family 
CANID.E.  The  Canid^  are  included  with  the  bears  (family 
IJRSiDiE),  the  seals  (family  Phocid^),  and  a  number  of  other 
groups  of  flesh-eating  animals  in  the  order  Carnivora.  Fifteen 
related  orders,  of  which  the  Carnivora  forms  one,  are  placed  in 
the  class  Mammalia.  Mammals  possess  hair  and  mammary 
glands;  these  characteristics  distinguish  them  from  the  five 
other  classes  that  make  up  the  subphylum  Vertebrata,  or  ani- 
mals possessing  vertebral  columns.  The  subphylum  Verte- 
brata, together  with  three  other  subphyla,  usually  called 
primitive  vertebrates,  are  grouped  under  the  phylum  Chordata, 
which  contains  animals  possessing  at  some  time  in  their  existence 
an  internal  rod-like  support  known  as  the  notochord. 

The  scientific  name  of  any  animal  consists  of  the  terms  used 
to  designate  the  genus  and  species;  this  is  commonly  followed 
by  the  name  of  the  zoologist  who  wrote  the  first  authori- 
tative description  of  that  particular  species.  The  scientific 
name  of  the  gray  wolf  is  therefore  written  Canis  occidentalis 
Richardson. 

The  complete  classification  of  the  gray  wolf  may  be  shown  in 
outline  in  the  following  manner:  — 

Phylum  Chordata 
Subphylum  Vertebrata 
Class  Mammalia 
Order  Carnivora 
Family  Canid^e 
Genus  Canis 
Species  occidentalis  Richardson. 

Zoologists  do  not  agree  as  to  the  exact  meaning  of  the  term 
species.     One   authority   gives   the    following   definition:     "A 


INTRODUCTION  23 

species  may  be  defined  as  a  group  of  interbreeding  individuals 
which,  while  they  may  differ  markedly  among  themselves,  yet 
resemble  each  other  more  closely  than  they  do  those  of  any  other 
group;  the  characters  that  distinguish  the  group  being  consid- 
erable, not  obliterated  by  intermediate  forms,  and  inherited  from 
generation  to  generation." 

*>■ 

8.  The  Principal  Phyla  of  the  Animal  Kingdom  ^JL^  -   . 

The  principal  phyla  of  the  animal  kingdom  as  outlined  in  the 
following  paragraphs  are  presented  in  this  place  since  they  will  ^ 
be  of  value  for  reference  purposes  during  the  perusal  of  the  more     ^^ 
detailed  accounts  in   the   succeeding  chapters.     The  numbers     3=-, 
after  each  phylum  indicate  approximately  the  number  of  living 
species  known  at  the  present  time.^    The  groups  of  animals  of      / 
more  or  less  uncertain  systematic  position  have  been  omitted 
from  this  outline  (see  Chap,  IX). 

(i)  Protozoa.  —  Single-celled  animals;  often  colonial;  sperm 
and  egg  cells  usually  wanting.     8500. 

(2)  Porifera.  —  Sponges.  Diploblastic  (?) ;  radially  symmet- 
rical, number  of  antimeres  variable ;  body-wall  permeated  by 
many  pores  and  usually  supported  by  a  skeleton  of  spicules  or 
spongin.     2500. 

(3)  Coelenterata.  —  Jellyfishes,  Polyps,  and  Corals.  Diplo- 
blastic; radially  symmetrical,  with  usually  four  or  six  anti- 
meres; single  gastro- vascular  cavity;  no  anus;^  body-wall  con- 
tains peculiar  structures  known  as  nematocysts  or  stinging  cells. 
4200. 

(4)  Ctenophora.  —  Sea  Walnuts  or  Comb  Jellies.  Triplo- 
blastic;  radial  combined  with  bilateral  symmetry;  eight  radially 
arranged  rows  of  paddle  plates.     100. 

(5)  Platyhelminthes.  —  Flatworms.  Triploblastic;  bilaterally 
symmetrical;  single  gastro- vascular  cavity;  no  anus;  presence 
of  coelom  doubtful.     4600. 

^I  am  indebted  to  Professor  Henry  S.  Pratt  for  the  numbers  given. 


24  COLLEGE  ZOOLOGY 

(6)  Nemathelminthes. — Thread  Worms.  Triploblastic;  bi- 
laterally symmetrical;  possess  a  tubular  digestive  system  with 
an  anus;  coelom  present.     1500. 

(7)  Echinodermata.  —  Starfishes,  Sea  Cucumbers,  Sea  Ur- 
chins, Sea  Lilies.  Triploblastic;  radially  symmetrical;  usually 
five  antimeres;  coelom  well  developed;  anus  usually  present; 
locomotion  in  many  species  accomplished  by  characteristic  organs 
known  as  tube  feet;  a  spiny  skeleton  of  calcareous  plates  gen- 
erally covers  the  body.     3000. 

(8)  Annelida. — Jointed  Worms.  Triploblastic;  bilaterally 
symmetrical;  coelom  well  developed;  anus  present;  segmented, 
somites  similar.     4000. 

(9)  Mollusca.  —  Clams,  Snails,  Devilfishes.  Triploblastic; 
bilaterally  symmetrical;  anus  and  coelom  present;  no  segmenta- 
tion; shell  usually  present;  the  characteristic  organ  is  a  ventral 
muscular  foot.     60,000. 

(10)  Arthropoda.  —  Crabs,  Insects,  Spiders,  Centipedes, 
Scorpions,  Ticks.  Triploblastic ;  bilaterally  symmetrical ; 
anus  present;  coelom  poorly  developed;  segmented,  somites 
usually  more  or  less  dissimilar ;  paired,  jointed  appendages 
present  on  all  or  a  part  of  the  somites;  chitinous  exoskeleton. 
400,000. 

(11)  Chordata. — Amphioxus,  Sea  Squirts,  Vertebrates. 
Triploblastic;  bilaterally  symmetrical;  anus  and  coelom  present; 
segmented;  gill  slits  and  a  rod  called  the  notochord  present  in 
some  stage  of  life  history;  central  nervous  system  on  dorsal  side 
of  alimentary  canal.     30,000. 

Zoologists  do  not  agree  as  to  the  number  of  phyla  into  which 
the  animal  kingdom  should  be  divided.  Some  authorities  recog- 
nize only  eight,  while  others  maintain  that  there  should  be  as 
many  as  twenty,  or  even  more.  Two  sub-kingdoms  are  generally 
recognized.  Protozoa  (Phylum  i)  and  Metazoa  (Phyla  2-1 1). 
Recently  many  zoologists  have  come  to  believe  that  the  sponges 
(Phylum  2)  should  be  separated  from  other  Metazoa  and  called 
the  Parazoa. 


INTRODUCTION 


25 


Figure  8  shows  by 
this  is  modified  from 
II,  p 


a  diagram  one  method  of  classification; 
Lankester's  ''  Treatise  on  Zoology,"  Part 


2. 


4.  Phylum  Ctenophora 
3.  Phylum  Coelenterata 


II. 

Phylum  Chordata 

10. 

Phylum  Mollusca 

9. 

Phylum  Arthropoda 

8. 

Phylum  Annelida 

7- 

Phylum  Echinodermata 

6. 

Phylum  Nemathelminthes 

5- 

Phylum  Platyhelminthes 

Enteroccela 

(Animals  with  single 
body  cavity,  the 
enteron) 


Phylum  Porifera 

Parazoa 
(Sponges) 


CCELOMOCCELA 


(Animals  with  two 
body  cavities,  en- 
teron and  coelom) 


Enterozoa 


(Primitively  a  dou- 
ble-walled sac  with 
a  single  external 
opening) 


Metazoa 
(Many-celled  animals) 

I 

I.  Phylum  Protozoa 
(One-celled  animals) 

Fig.  8.  —  Classification.     Diagram  showing  one  way  of  classifying  animals. 


9.  Zoology  and  its  Subsciences 

Zoology  is  the  science  of  animals,  but  the  facts'  about  animals 
and  the  methods  of  studying  them  have  become  so  numerous 
that  one  man  in  his  lifetime  can  master  and  become  an  authority 
on  only  one,  or  at  most  a  few  phases  of  the  subject.  It  has, 
therefore,  been  found  necessary  and  convenient  to  divide  Zoology 
into  subsciences.  The  principal  subsciences  are  named  and  very 
briefly  defined  in  Table  II. 


26 


COLLEGE  ZOOLOGY 


-^ 


^ 


o  B 

v_^     CO 

^  H 

I 

o 


a    o 


en 


to 

o 


IS 


TABLE  II 

ZOOLOGY  AND  ITS   SUBSCIENCES 

Anatomy  (Or.  anatemno,  cut  up). 

The  study  of  the  structure  of  organisms  as  made 
out  by  dissection. 

Histology  (Or.  histos,  tissue;  logos,  discourse). 
The  study  of  the  microscopic  structure  of  tissues. 

Taxonomy  (Or.  taxis,  arrangement;  nomos,  law). 
The  study  of  the  laws  and  principles  of  classification. 

Zoogeography  (Or.  zoon^  animal;  geography). 

The  study  of  the  geographical  distribution  of  animals. 

Paleontology    (Or.   palaios,   ancient ;     onta,   beings; 
logos,  discourse). 
The  study  of  fossil  organisms. 

Teratology  (Or.  teras,  wonder,  logos,  discourse). 
The  study  of  malformations  and  monstrosities  in 
organisms. 

Phylogeny  (Or.  phylon,  tribe;  gennao,  produce). 

The  study  of  the  ancestral  history  of  organisms. 
Embryology  (Or.  en,  in;  hruo,  bud). 

The  study  of  the  early  developmental  stages  of 
animals. 

Pathology  (Or.  pathos,  suffering;  logos,  discourse). 
The  study  of  the  nature  of   diseases,   and  their 
causes  and  symptoms. 

Physiology  (Or.  phusis.  nature;  logos,  discourse). 
The  study  of  the  functions  of  organisms. 

Ecology  (Or.  oikos,  house;  logos,  discourse). 

The  study  of  the  relations  of  organisms  to  their 
environment. 

Psycnology  (Or.  psiiche,  mind;  logos,  discourse). 
The  study  of  the  mind. 

Sociology  (L.  socius,  companion;  logos  discourse). 
The  study  of  animal  societies. 


CHAPTER  II 
PHYLUM  PROTOZOA 

The  Protozoa  (Gr.  protos,  first;  zoon,  an  animal)  are  mostly 
microscopic  animals,  although  some  of  the  commonest  species, 
like  Paramecium  (Fig.  2)i)j  are  visible  to  the  naked  eye.  They 
are  the  simplest  of  all  animals,  consisting  of  but  a  single  cell. 
Nevertheless,  most  of  the  activities  characteristic  of  the  many- 
celled,  complex  animals  are  exhibited  by  them,  usually  in  a  sim- 
pler form.  In  many  cases  Protozoa  are  colonial;  that  is,  a 
number  of  individuals  of  one  species  are  more  or  less  intimately 
associated  into  a  colony  (Fig.  29). 

The  Protozoa  are  separated  into  classes  according  to  the 
presence  or  absence  of  locomotor  organs  and  the  character  of 
these  when  present.     Four  classes  are  usually  recognized: 

Class  I.  Rhizopoda  (Gr.  rhiza,  a  root;  pous,  a  foot),  with 
pseudopodia  (Fig.  9,  j); 

Class  II.  Mastigophora,  (Gr.  mastix,  whip;  phero,  bear) 
with  flagella  (Fig.  22); 

Class  III.  Sporozoa  (Gr.  spora,  seed;  zoon,  animal),  with- 
out locomotor  organs  in  adult  stage  (Fig.  32);  and 

Class  IV.  Infusoria  (Lat.  infusus,  poured  into,  crowded  in), 
with  cilia  (Fig.  33). 

I.   Class  I.    Rhizopoda 

a.  Ameba  proteus 

The  fresh-water  Protozoon,  Ameba  proteus  (Fig.  9),  is  usually 
selected  as  a  type  of  the  class  Rhizopoda.  It  is  only  about  you 
inch  in  diameter,  and  is  therefore  invisible  to  the  naked  eye. 

27 


28 


COLLEGE  ZOOLOGY 


Under  the  compound  microscope  Ameba  looks  like  an  irregular 
colorless  particle  of  animated  jelly.  The  best  way  to  obtain 
specimens  for  laboratory  use  is  to  collect  a  mass  of  pond  weed 
(preferably  Ceratophyllum),  place  it  in  a  fiat  dish,  and  immerse 
in  water.  The  brown  scum  which  appears  on  the  surface  in  a 
few  days  generally  contains  many  AmebcB. 

Anatomy.  —  Two  regions  are  distinguishable  in  the  body  of 
Ameba,  the  ectosarc  and  the  endosarc.     The  ectosarc  (Fig.  9,  j), 


Fig.  9.  —  Ameba  protcus.  i,  nucleus;  2,  contractile  vacuole;  3,  pseudopodia, 
dotted  line  leads,  to  ectoplasm;  4,  food  vacuoles;  5,  grains  of  sand.  (From 
Shipley  and  MacBride,  after  Gruber.) 


which  consists  of  ectoplasm,  is  the  outer  colorless  layer.  It  is 
firmer  than  the  endosarc  and  is  free  from  granules.  The  endo- 
sarc is  the  large  central  mass  of  granular  protoplasm.  Within 
it  lies  the  nucleus  (Fig.  9,  i),  which  is  difficult  to  find  in  living 
Amebce,  but  can  easily  be  made  out  in  animals  that  have  been 
properly  killed  and  stained.  The  nucleus  is  necessary  for  the 
life  of  the  animal,  since  if  an  individual  is  cut  in  two  the  part 
with  the  nucleus  survives,  whereas  the  enucleated  fragment  dies. 


PHYLUM   PROTOZOA 


29 


It  probably  plays  an  important  role  in  the  metabolic  activity  of 
the  cell. 

A  clear  space  filled  with  a  fluid  less  dense  than  the  surrounding 
protoplasm  may  be  seen  in  favorable  specimens.  It  is  called  the 
contractile  v^,g4iilg^  (Fig.  9,  2),  since  its  walls  contract  at  more  or 
less  regular  intervals  and  force  the^iluid  contents  out  of  the  body. 
It  serves  to  get  rid  of  the  water  taken  in  through  the  surface  of 
the  body,  thus  regulating  the  tension  between  the  protoplasm 
and  the  surrounding  medium.  It  is  also  considered  a  primitive 
excretory  organ. 

The  solid  particles  of  food  engulfed  by  Ameha  cause  the  for- 
mation of  foodv^ifiiple^  (Fig.  9,  4),  which  are  temporary  structures 
for  the  digestion  of  organic  material.  Besides  the  nucleus,  con- 
tractile vacuole,  and  usually  one  or  more  food  vacuoles,  there  are 
often  undigested  particles,  and  foreign  substances,  like  grains 
of  sand  (Fig.  9,  5) ,  embedded  in  the  endoplasm. 

Metabolism.  —  Metabolism  is  the  term  applied  to  the  series 
of  processes  concerned  with  the  manufacture  and  breaking  down 
of  protoplasm.  The  term  anaholism  is  used  for  the  constructive 
processes  such  as  the  ingestion,  digestion,  absorption,  and  as- 
similation of  food.  The  term  ka^ol^'m  means  the  breaking 
down  of  protoplasm  into  simpler  products,  and  includes  the 
processes  of  secretion,  excretion,  and  respiration. 

Food.  —  The  food  of  Ameba  consists  of  very  small  aquatic 
plants,  such  as  Oscillaria  and  diatoms.  Protozoa,  Bacteria, 
and  other  animal  and  vegetable  matter.  A  certain  amount  of 
choice  of  food  is  exercised,  or  the  Amehd's  body  would  become 
overloaded  with  particles  of  sand  and  other  indigestible  mate- 
rial among  which  it  lives. 
_lNGESlKtN:j(Fig.  10).  — The  ingestion  or  taking  in  of  food  oc- 
curs without  the  aid  of  a  mouth.  Food  may  be  engulfed  at  any 
point  on  the  surface  of  the  body,  but  it  is  usually  taken  in  at 
what  may  be  called  the  temporary  anterior  end,  that  is,  the  part 
of  the  body  toward  the  direction  of  locomotion.  A  small  amount 
of  water  is  taken  in  with  the  food,  so  that  there  is  formed  a 


30 


COLLEGE  ZOOLOGY 


vacuole  whose  contents  consist  of  a  particle  of  nutritive  material 
suspended  in  water.  The  whole  process  of  food-taking  occupies 
one  or  more  minutes,  depending  on  the  character  of  the  food. 
No  doubt  the  reactions  in  food-taking  depend  upon  both  me- 
chanical and  chemical  stimuli. 

Imitations  of  the  engulfing  of  food  by  Ameba  have  been  de- 
vised, based  on  the  theory  that  ingestion  depends  on  the  physical 


Fig.  io.  —  Ameba  ingesting  a  Euglena  cyst,     i,  2,  3,  4,  successive  stages 
in  the  process.     (From  Jennings.) 


adhesion  between  the  liquid  protoplasm  and  the  solid  food. 
Drops  of  water,  glycerin,  white  of  egg,  etc.,  will  draw  into  con- 
tact and  engulf  solid  particles  of  various  kinds. 

Digestion.  —  Digestion  takes  place  without  the  aid  of  a 
stomach.  After  a  food  vacuole  has  become  embedded  in  the 
endoplasm,  a  secretion  of  some  mineral  acid,  probably  HCl, 
enters  through  the  walls  of  the  vacuole.  This  digestive  fluid 
seems  to  dissolve  only  proteid  substances,  having  no  effect  upon 
fats  and  carbohydrates. 

Egestion.  —  Undigested  particles,  the  faeces,  are  egested  at 
any  point  on  the  surface  of  the  Ameba,  there  being  no  special 
opening  to  the  exterior  for  this  waste  matter.  Usually  such 
particles  are  heavier  than  the  protoplasm,  and,  as  the  animal 
moves  forward,  they  lag  behind,  finally  passing  out  at  the  end 


PHYLUM   PROTOZOA  3 1 

away  from  the  direction  of  movement;  that  is,  Ameha  flows 
away,  leaving  the  undigested  solids  behind. 

AssiMiLAtiON.  —  The  peptones,  derived  from  the  digestion 
of  proteid  substances,  together  with  the  water  and  mineral 
matter  taken  in  when  the  food  vacuole  was  formed,  are  absorbed 
hy  the  surrounding  protoplasm,  and  pass  into  the  body  substance 
of  the  animal,  no  circulatory  system  being  present,  so  far  as  we 
know.  These  particles  of  organic  and  inorganic  matter  are  then 
assimilated;  that  is,  they  are  rearranged  to  form  new  particles 
of  living  protoplasm,  which  are  deposited  among  the  previously 
existing  particles.  The  ability  to  thus  manufacture  protoplasm 
from  unorganized  matter,  it  will  be  remembered,  is  one  of  the 
fundamental  properties  of  living  substance  (p.  10). 

Katabolism. — The  energy  for  the  work  done  by  Ameha 
comes  from  the  breaking  down  of  complex  molecules  of  proto- 
plasm by  oxidation  or  "  physiological  burning."  This  is  known 
as  katabolism  or  dissimilation.  The  products  of  this  slow  com- 
bustion are  the  energy  of  movement,  heat,  and  residual  matter. 
This  residual  matter  ordinarily  consists  of  solids  and  fluids, 
mainly  water,  some  mineral  substances,  urea  and  carbon  dioxide. 
Secretions,  excretions,  and  the  products  of  respiration  are  in- 
cluded in  this  list. 

Secretion.  —  We  have  already  noted  that  an  acid  is  poured 
into  the  gastric  vacuole  by  the  surrounding  protoplasm.  Such 
a  product  of  dissimilation,  which  is  of  use  in  the  economy  of  the 
animal,  is  known  as  a  secretion. 

Excretion.  —  Materials  representing  the  final  reduction  of 
substances  in  the  process  of  katabolism  are  called  excretions. 
These  are  deposited  either  within  or  outside  of  the  body.  A  large 
part  of  the  excretory  matter,  including  urea  and  carbon  dioxide, 
passes  through  the  general  surface  of  the  body.  The  fluid  con- 
tents of  the  contractile  vacuole  are  known  to  contain  urea,  there- 
fore this  organ  is  excretory  in  function. 

Respiration. — The  contractile  vacuole  is  also  respiratory, 
since  carbon  dioxide  probably  makes  its  way  to  the  exterior  by 


32  COLLEGE  ZOOLOGY 

way  of  this  organ.  Oxygen  dissolved  in  water  is  taken  in  through 
the  surface  of  the  body.  This  gas  is  necessary  for  the  Hfe  of  the 
animal ;  if  replaced  by  hydrogen,  movements  cease  after  twenty- 
four  hours;  if  air  is  then  introduced,  movements  begin  again; 
if  not,  death  ensues. 

Growth.  —  If  food  is  plentiful,  more  substance  is  added  tqi 
the  living  protoplasm  of  the  Ameba  than  is  used  up  in  its  various 
physical  activities.  The  result  is  an  increase  in  the  volume  of 
the  animal.  This  is  growth,  and,  as  in  all  other  living  organisms, 
growth  by  the  addition  of  new  particles  among  the  preexisting 
particles,  i.e.  growth  by  intussusception. 

Reproduction.  —  There  is,  however,  a  limit  with  regard  to  the 
size  that  may  be  attained  by  Ameba  proteus,  as  it  rarely  exceeds 
.25  mm.  {j^-Q  inch)  in  diameter.  When  this  limit  is  reached  the 
animal  divides  into  two  parts.  Why  should  there  be  such  a 
limit?  The  following  explanation  is  given  by  Herbert  Spencer 
and  others.  Xb^^^'Ql^^^^^  of  an  organism  varies  aa  the  cube  of 
its  diameter^  the  surface  as  the  square.  Thus,  as  an  animal 
grows,  the  ratio  between  surface  and  volume  decreases;  and, 
since  Ameba  takes  in  food,  gives  off  waste  material,  and  carries 
on  respiration  through  its  surface,  the  activities  of  the  cell  must 
decrease  with  increase  in  size  until  further  growth  is  impossible. 
The  solution  of  the  problem  is  the  division  of  the  animal  into 
two,  whereby  the  ratio  of  surface  to  volume  is  increased.  Re- 
production by  binary  division,  therefore,  takes  place  when 
growth  is  no  longer  possible.  It  is  supposed  that  this  division 
is  inaugurated  through  some  unknown  change  in  the  relations 
between  the  nucleus  and  cytoplasm.  There  are  at  least  two 
kinds  of  reproduction  in  Ameba  proteus,  but  neither  has  ever 
been  satisfactorily  worked  out  in  detail.  They  are  (i)  binary 
division  and  (2)  sporulation. 

(i)  During  binary  division  (Fig.  11)  the  nucleus  divides  by  a 
primitive  sort  of  mitosis.  Then  the  animal  elongates,  a  constric- 
tion appears  near  the  center,  and  division  into  two  daughter  cells 
finally  takes  place. 


PHYLUM   PROTOZOA 


33 


(2)  Sporulation  is  apparently  a  rare  process  of  multiplication  in 
Ameba.  First  the  pseudopodia  are  drawn  in  and  the  animal 
becomes  spherical;  a  three-layered  cyst  is  then  secreted.  By 
successive  divisions  of  the  nucleus  from  five  hundred  to  six 
hundred  daughter  nuclei  are  produced.     Cell  walls  then  appear, 


Fig.  II. 


Ameba  polypodia  dividing  by  binary  fission. 
Haswell,  after  F.  E.  Schulze.) 


(From  Parker  and 


dividing  the  Ameba  into  as  many  cells  as  there  are  nuclei.  These 
Amebulce,  or  pseudopodiospores,  as  they  are  sometimes  called, 
break  out  through  the  cyst  and  become  recognizable  as  Ameba 
proteus  in  about  three  weeks. 

The  Behavior  of  Ameba.  —  The  sum  total  of  all  the  move- 
ments of  an  animal  constitute  what  is  know^n  as  its  behavior. 
In  Ameba  these  movements  may  be  separated  into  those  con- 

D 


34  COLLEGE  ZOOLOGY 


^^•: 


nected  with  locomotion  and  those  resulting  from  external  and 
internal  stimuli. 

J^pcoMOTiON.  —  Ameba  moves  from  place  to  place  by  means 
of  finger-like  protrusions  of  the  body,  known  as  pseudopodia 
(Fig.  9,  j).  A  pseudopodium  is  formed  in  the  following  manner. 
The  ectoplasm  bulges  out  and  enlarges  until  a  blunt  projection 
is  produced;  the  endoplasm  then  flows  into  it.^J  The  result  is 
a  movement  of  the  entire  animal  in  the  direction  of  the  pseudo- 
podium. If  more  than  one  are  formed  at  the  same  time,  there 
occurs  a  struggle  for  supremacy  until  finally  one  survives  while 
the  others  flow  back  and  gradually  disappear.  Ameba  moves, 
therefore,  by  thrusting  out  pseudopodia  and  then  flowing  into 
them. 

There  are  three  principal  theories  which  attempt  to  explain 
the  formation  of  pseudopodia.  (i)  The  adherence  theory  holds 
that  the  pseudopodium  adheres  on  one  side  more  strongly  than 
on  the  others,  and  that  the  entire  animal,  therefore,  moves  to- 
ward the  adhering  side.  (2)  The  surface  tension  theory  maintains 
that  local  changes  in  the  surface  tension  cause  the  currents  which 
initiate  movement.  (3)  According  to  the  contractile  theory^ 
Ameba  moves  by  means  of  a  contractile  substance  in  the  follow- 
ing manner.  In  advancing  the  Amebce  "  extend  the  anterior 
end  free  in  the  water  and  attach  it  at  or  near  the  tip  and  then 
contract.  At  the  same  time  the  posterior  end  is  contracting 
and  the  substance  thus  pushed  and  pulled  forward  goes  to  form 
the  new  anterior  end  (Fig.  12,  A,  B).  .  .  .  In  other  cases 
the  anterior  end  is  lifted  free  and  then  curves  down  to  the  sub- 
stratum and  attaches,  forming  a  long  loop.  The  posterior  end 
is  then  released,  and  the  substance  flows  over  to  the  anterior 
end.  At  the  same  time  another  anterior  end  is  extended  (Fig. 
12,  C)." 

There  are  various  methods  of  imitating  the  movements  of  Ameba 
by  means  of  inorganic  substances.  One  of  these  is  as  follows: 
A  large  drop  of  mercury  is  placed  in  a  flat-bottomed  watch 
glass  and  covered  with   10  per  cent  nitric  acid.     A  piece  of 


PHYLUM   PROTOZOA 


35 


potassium  bichromate  when  placed  near  the  mercury  produces 
a  solution  which  causes  local  lowering  of  the  surface  tension  of 


'^ 


J 


Fig.  12.  —  Locomotion  of  Amcba  proteus.  Photographs  in  side  view.  A 
and  B  show  a  specimen  attached  at  two  points,  a  and  b,  and  a  pseudopod  which 
projects  from  one  end  and  bends  down  to  the  substratum  as  in  B  at  ti;  C  shows 
the  extension  of  a  long  pseudopod.     (From  Bellinger  in  Journ.  Exp.  Zool.) 


the  drop,  and  results  in  the  formation  of  projections  and  move- 
ment of  the  mercury  in  various  directions. 
-^,  Reactions  to  Stimuli.  —  A  turning  of  an  animal  resulting 
from  a  change  in  its  environment,  for  example  an  increase  in 
the  intensity  of  the  light,  is  known  as  a  ^'tropism'^  or  "taxis.'* 


36  COLLEGE  ZOOLOGY 

The  term  "  tropism  "  means  "  a  turning  ";  it  is  used  for  purely 
descriptive  purposes.  Nothing  is  known  of  the  psychic  phe- 
nomena of  the  lower  animals,  and  one  must  be  cautious  in  at- 
tributing to  them  his  own  mental  states.  The  term  "  tropism  '* 
merely  describes  an  animal's  behavior  in  response  to  stimuli. 
The  kind  of  stimulus  employed  is  indicated  by  a  prefix.  The 
principal  kinds  of  tropisms  are  as  follows:  — 

(i)  Thigmo tropism  =  reaction  to  contact. 

(2)  Chemotropism  =  reaction  to  a  chemical. 

(3)  Thermotropism  =  reaction  to  heat. 

(4)  Phototropism  =  reaction  to  light. 

(5)  Electro  tropism  =  reaction  to  electric  current. 

(6)  Geotropism  =  reaction  to  gravity. 

(7)  Chromo tropism  =  reaction  to  color. 

(8)  Rheotropism  =  reaction  to  current. 

"  Taxis  "  is  often  employed  instead  of  "  tropism,"  when  the 
terms  read  ''  thigmotaxis,"  "  chemotaxis,"  etc.  If  the  animal 
reacts  by  a  movement  toward  the  stimulus,  such  as  light,  it  is 
said  to  be  positively  phototropic  or  phototactic,  etc.;  if  away 
from  the  stimulus,  negatively  phototropic  or  phototactic,  etc. 
Ameha  has  been  found  to  respond  to  contact  with  solids,  to 
chemicals,  to  heat,  to  light,  to  colors,  and  to  electricity. 

Ameba  exhibits  negative  thigmotropism  when  touched  at  any 
point  with  a  solid  object;    the  part  affected  contracts  and  the 


Fig.   13.  —  Thigmotropism  of  Ameba.     The  animal  moves  away  when 
stimulated  by  a  glass  rod.     (From  Jennings.) 

animal  moves  away  (Fig.  13).     When,  however,  an  Ameha  is 
floating  freely  in  the  water  and  a  pseudopodium  comes  in  con- 


PHYLUM  PROTOZOA  37 

tact  with  the  substratum,  the  animal  moves  in  the  direction 
of  that  pseudopodium  until  the  normal  creeping  position  has 
been  attained.  Contact  with  food  also  results  in  positive  re- 
actions. Ameba,  therefore,  reacts  negatively  to  a  strong  me- 
chanical stimulus  and  positively  to  a  weak  one. 

Chemotropic  reactions  prove  that  ^meba  is  sensitive  to  changes 
in  the  chemical  composition  of  the  water  surrounding  it.  ''  It 
has  been  shown  to  react  negatively  when  the  following  sub- 
stances come  in  contact  with  one  side  of 
its  body;  methylene  blue,  methyl  green  »«  -* 
(Fig.  14),  sodium  chloride,  sodium  car-  ^'• 
bonate,  potassium  nitrate,  potassium 
hydroxide,  acetic  acid,  hydrochloric  acid, 
cane  sugar,  distilled  water,  tap  water,  ,Fig.  14.  —  Chemotro- 
and  water  from  other  cultures  than  that  marmoveT^away  when^a 
in  which  the  Amosba  under  experimenta-     little  methyl  green  diffuses 

-.  ,,  against  the  advancing  end. 

tion  lives.  (From  Jennings.) 

Negatively  thermotropic  reactions  result 
if  Ameba  is  locally  affected  by  heat,  since  the  animal  will  move 
away  from  heat  stimuli.     Cold  and  excessive  heat  retard  its 
activities,  which  cease  altogether  between  30°  and  35°  C. 

Ameba  is  negatively  phototropic,  since  it  will  orient  itself  in 
the  direction  of  the  rays  of  a  strong  light  and  move  away  from 
it  (Fig.  15). 

In  Ameba  there  are  no  organs  that  can  be  compared  with  what 
we  call  sense  organs  in  higher  animals,  and  we  must  attribute  its 
reactions  to  stimuli  to  that  fundamental  property  of  protoplasm 
called  irritability.  The  superficial  layer  of  cytoplasm  receives 
the  stimulus  and  transfers  the  effects  to  some  other  part  of  the 
body;  thus  may  be  shown  the  phenomenon  of  internal  irritabil- 
ity or  conductivity.  The  stimulus  causing  a  reaction  seems  to 
be  in  most  cases  a  change  in  the  environment.  The  behavior  of 
Ameba  in  the  absence  of  external  stimuli,  for  example  when  it 
is  suspended  freely  in  the  water  (p.  36),  shows  that  some  of  its 
activities  are  initiated  by  internal  causes. 


33 


COLLEGE  ZOOLOGY 


,^1  /J  J  The  reactions  of  v4weia 

J2,  to    stimuli    are    of    un- 

doubted  value   to   the   individual 
and  to  the  preservation  of  the  race, 
for  the  negative  reaction  is  in  most 
cases  produced  by  injurious  agents 
such  as  strong  chemicals,  heat,  and 
mechanical  impacts,  whereas  posi- 
tive reactions  are  produced  usually 
by  beneficial  agents.     The  responses,  therefore,  in 
the  former  cases  carry  the  animal  out  of  danger, 
in  the  latter,  to  safety. 

Ameha  is  of  fundamental  interest  to  animal  psy- 
chologists, since  it  represents  the  "  animal  mind " 
in  its  most  primitive  form.  Whether  or  not  the 
animal  is  in  any  degree  conscious  is  a  question  still 
unanswered.  If  Ameba  has  recognizable  sensations, 
they  must  be  infinitely  less  in  both  quality  and 
quantity  than  those  of  higher  organisms.  Further- 
more, it  is  unable  to  learn  from  the  few  kinds  of 
experiences  it  does  pass  through,  and  is  therefore 
lacking  in  memory  images. 

A  review  of  the  facts  thus  far  obtained  seems  to 
show  that  factors  are  present  in  the  behavior  of 
Ameha  "  comparable  to  the  habits, 
reflexes,  and  automatic  activities  of 
higher  organisms,"  and  "  if  Amoeba 
were  a  large  animal,  so  as  to  come 
within  the  everyday  experience  of 
^'^-  J^'  -  Phototropism    j^^jnan  beings,   its  behavior  would  at 

ol  Ameba.    The  arrows  indi-  ,,^11  j_^  -i     j.-        4.      v      f 

cate  the  direction  of  the  light    once  Call  forth  the  attribution  to  It  ot 
rays  and  the  numbers  the    g^^^^g  ^f  pleasure  and  pain,  of  hunger, 

successive  positions  assumed  ,      ,        ,.,  •     1       4.1, 

by  the  animal.    The  Ameba    desire,  and  the  like,  on  precisely  the 
always   moves  away   from    game  basis  as  we  attribute  these  things 

the  source  of  light.      (From 

Jennings,  after  Davenport.)     tO  the  dog. 


PHYLUM  PROTOZOA 


39 


h.    Rhizopoda  in  General 

The  Protozoa  which  are  included  in  the  class  Rhizopoda 
have  been  grouped  into  four  principal  orders  according  to  the 
character  of  their  pseudopodia  and  the  structure  of  their  shells, 
if   these   are   present:    (i)   Lobosa,  (2)  Heliozoa,  (3)  Radio- 

LARIA,  (4)    FORAMINIFERA. 

Order  i.   Lobosa.    Rhizopoda  with  fingerlike  (lobose)  pseudo- 
podia.    Most  of  the  Lobosa  occur  in  fresh  water,  a  few  in 
moist  earth,  and  some  are  parasites. 
Examples:    Ameba   (Fig.   9),  Arcella  / 

(Fig.  16),  and  Difflugia  (Fig.  17).  ^^^ 

Arcella  (Fig.  16)  is  common  in  the 


Fig.  16.  —  Arcella  discoides  (order 
Lobosa)  as  seen  from  above,  i,  shell; 
2,  pseudopodia  ;  3,  edge  of  opening 
into  shell;  4,  thread  attaching  animal 
to  interior  of  shell;  5,  nucleus;  6,  food 
vacuole ;  7,  gas  vacuole.  (From 
Leidy.) 


Fig.  17. — Difflugia  urceo- 
lata  (order  Lobosa)  as  seen 
from  the  side,  i,  shell  com- 
posed of  minute  particles  of 
sand;  2,  pseudopodia.  (From 
Leidy.) 


ooze  on  the  bottoms  of  fresh-water  ponds  and  ditches.  It  has 
a  dome-shaped  brownish  shell  of  chitin  (j)  which  it  secretes. 
The  lobose  pseudopodia  (2)  protrude  from  a  circular  opening  (j) 
in  the  center  of  the  flattened  surface. 

Difflugia  (Fig.  17)  is  another  common  member  of  the  order 
Lobosa,  and  is  also  found  in  the  ooze  of  ponds.  Its  shell  (7) 
consists  of  minute  particles  of  sand  and  other  foreign  objects 
held  together  by  chitin. 


40 


COLLEGE  ZOOLOGY 


Order    2.     Heliozoa.  —  Rhizopoda  with  thin,    radially   ar- 
ranged  pseudopodia,    which   are   usually    supported   by   axial 

threads  (Fig.  18,  a).  Ex- 
amples: ActinosphcBrium,  Ac- 
tinophrys  (Fig.  18). 

Actinophrys  (Fig.  18),  the 
sun  animalcule,  lives  among 
the  aquatic  plants  in  fresh- 
water ponds  and  ditches.  The 
body  appears  vesicular,  being 
crowded  with  vacuoles  (c). 
The  small  organisms  which 
serve    as    food     strike    the 

pseudopodia,   pass   down   to 
Fig.  18.  —  Actinophrys  sol,   a  Helio-    .111  j  u-    1 

zooN.    An  individual  with  a  large  gastric  ^hc  body,  and  are  cngulfed; 
vacuole  {g),  contractile  vacuole  (c),  and  larger  Organisms  (^)  are  drawn 

axial  filaments  (a)  in  the  ravHke  pseudo-    .        ,  ,  •   i  i       • 

podia.     (From  Calkins,  after  Grenacher.)    ^"^     by     several  ^  neighbormg 

pseudopodia  acting  together. 

Order  3.  Radiolaria.  —  Marine  Rhizopoda  with  raylike 
pseudopodia,  a  central  perfor- 
ated capsule  of  chitin  (Fig.  19, 
sk.  j),  and  usually  a  larger  en- 
closing skeleton  of  silica  {sk.  i, 
sk.2).  Examples:  Actinomma 
(Fig.  19),  Thalassicolla,  Heli- 
osphcera. 

The  shells  of  the  radio- 
larians,  upon  sinking  to  the 
sea  bottom,  form  radiolarian 
ooze;  this  becomes  hardened, 
producing  rock  strata  as  much 
as    1000    feet    thick.     These  ,  ^^^'^''^'J^T'Sl 

rocks    may   take    the    form    of   away  so  as  to  show  the  outer   {sk.  i), 

miartzitp^    flint    or   rhprt   ron-   "^^^dle  {sk.  2),  and  inner  {sk.  3)  spheres. 
quartZltes,  nmt,  or   cnert   con-    ^.^^^^     Weysse,     after     Haeckel     and 

cretions.  Hertwig.) 


Sh.2 


PHYLUM    PROTOZOA 


41 


Order  4.  Foraminif  era. — Rhizopoda,  mostly  marine,  with  fine, 
branching  pseudopodia  which  fuse  forming  a  protoplasmic  net- 
work.    Examples:  Allogromia  (Fig.  20),  Globigerina,  Discorhina. 

Allogromia  (Fig.  20)  lives  in 
fresh  water  and  has  a  chitinous 
shell ''■(5/^.).  The  shells  of  many 
FoRAMiNiFERA  consist  of  numer- 
ous chambers  connected  by  open- 
ings (foramina),  and  are  com- 
posed of  calcium  carbonate. 
When  these  shells  sink  to  the  sea- 
bottom,  they  become  Globigerina 
ooze,  which  solidifies,  forming 
gray  chalk  (Fig.  21). 


Fig.  20.  —  Allogromia  {oxAex  For- 
aminifera).  a,  aperture  of  shell; 
sh,  shell.  (From  the  Cambridge 
Natural  History.) 


Fig.  21.  —  FoRAMiNiFERA.  Shells 
as  they  exist  in  gray  chalk.  (From 
Scott,  after  a  photograph  by  the 
Geological  Survey  of  Iowa.) 


2.  Class  II.    Mastigophora 
a.   Euglena  viridis 


Euglena  viridis  (Fig.  22)  is  a  small  greenish  Protozoon  which 
will  serve  to  point  out  the  characteristics  of  the  Mastigophora. 
It  lives  in  small  bodies  of  fresh  water,  and  may  appear  in  ameba- 
cultures  (p.  28). 


Fig.  22.  —  Euglena  viridis.  A,  view  of  free-swimming  specimen  showing 
details  of  structure;  B,  another  animal  showing  change  of  shape  and  striations; 
C  and  D,  outlines  showing  stages  of  contraction;  E,  reproduction  by  longi- 
tudinal fission;  F  and  G,  division  within  a  cyst;  am,  pyrenoids  with  sheaths 
of  paramylum;  chr,  chromatophores;  c.v,  contractile  vacuoles;  e,  stigma  or 
eye-spot;  m,  mouth;  n,  nucleus;  r,  reservoir.  (A-D,  from  Bourne;  E-G 
from  Bourne,  after  Stein.) 


PHYLUM   PROTOZOA 


43 


Anatomy.  —  Euglena  (Fig.  22)  is  a  simple  elongated  cell,  and, 
although  somewhat  elastic,  maintains  a  more  or  less  constant 
shape.  It  possesses,  in  addition  to  ectosarc  and  endosarc,  a  thin 
outer  membrane,  the  cuticle,  which  is  striated,  as  shown  in  Figure 
22,  B.  Near  the  center  of  the  anterior  end  is  a  long  slender 
whiplike  process,  the  flagellum,  which  extends  out  from  an  open- 
ing called  the  mouth  (Fig.  22,  A,  m).  From  the  mouth  a  tubular 
"  gullet  "  leads  to  a  permanent  vesicle,  the  reservoir  {A,  r)\  into 
this  reservoir  several  contractile  vacuoles  {A,  cv)  discharge  their 
contents.  Close  to  the  reservoir  is  a  protoplasmic  mass  con- 
taining granules  of  a  red  coloring  matter,  hcematochrome ;  this 
is  called  the  stigma  or  eye-spot  {A ,  e)  because  it  is  supposed  to  be 
especially  sensitive  to  light.  Near  the  center  of  the  body  is 
a  nucleus  {A,n),  and  scattered  about  in  the  protoplasm  are  many 
oval  bodies,  greenish  in  color,  called  chromatophores  {A,  chr). 

Physiology.  —  Nutrition.  —  Euglena  probably  does  not 
ingest  solid  particles  by  means  of  the  mouth  and  gullet,  but 
manufactures  its  own  food  by  the  aid  of  the  chlorophyll  contained 
in  the  chromatophores.  As  in  plants,  this  chlorophyll  is  able, 
in  the  presence  of  light,  to  break  down  the  carbon  dioxide  (CO2), 
thus  setting  free  the  oxygen,  and  to  unite  the  carbon  with  water, 
forming  a  substance  allied  to  starch,  called  paramylum  (Fig.  22, 
A  and  B,  am).  This  mode  of  nutrition  is  known  as  holophytic. 
Some  organic  substances  are  probably  absorbed  through  the 
surface  of  the  body,  that  is,  saprophytic  nutrition  supplements 
the  holophytic.  Euglena  differs  from  most  animals  in  its  method 
of  nutrition,  since  the  majority  of  them  ingest  solid  particles  and 
are  said  to  be  holozoic. 

Behaviour.  —  Locomotion.  —  Euglena  because  of  its  elastic- 
ity is  able  to  squirm  through  small  openings,  but  its  chief  method 
of  locomotion  is  swimmin'g.  The  flagellum,  consisting  of  four 
contractile  fibrils  which  are  wound  together  spirally,  bends  to 
and  fro,  drawing  the  animal  along. 

Reactions  to  Stimuli.  —  Euglena  is  very  sensitive  to  light, 
and  is  a  favorable  object  for  the  study  of  phototropism.    It 


44  COLLEGE  ZOOLOGY 

swims  toward  an  ordinary  light  such  as  that  from  a  window,  and 
if  a  culture  containing  Euglence  is  examined,  most  of  the  ani- 
mals will  be  found  on  the  brightest  side.  This  is  of  distinct 
advantage  to  the  animal,  since  light  is  necessary  for  the  assimi- 
lation of  carbon  dioxide  by  means  of  its  chlorophyll.  If  a  drop 
of  water  containing  Euglence  is  placed  in  the  direct  sunlight  and 
then  one  half  of  it  is  shaded,  the  animals  will  avoid  the  shady 
part  and  also  the  direct  sunlight,  both  of  which  are  injurious  to 

them,  and  will  remain  in  a 
small  band  between  the  two 
in  the  light  best  suited  for 
them,  that  is,  their  optimum 
(Fig.  23).  By  shading  various 
portions  of  the  body  of  a 
Euglena  it  has  been  found 
that  the  region   in   front  of 

Fig.   23.  —  Phototropism  of   Euglena.  ,,                          .                 cptmitive 

Diagram  showing  the  reaction  of  EuglencB  ^^^  eye-SpOt  IS  morC  Sensitive 

to  light.    The  light  comes  from  the  direc-  than      any     Other     part.        It 

tions  indicated  by  the  arrows,  while  the  i_iiv             ij^i.^        1. 

opposite  side  of  the  vessel  is  shaded,  as  ^hould    be    noted    that    when 

indicated   by   the   dots.      The    Euglence  EuglencB     are      Swimming 

gather  in  the  intermediate  region  across  ,-i            i,    at_            a.        •*.    •      at_' 

the  middle.     (From  Jennings.)  through   the   water    it   IS   thlS 

anterior  end  which  first 
reaches  an  injurious  environment;  the  animals  give  the  avoiding 
reaction  at  once,  and  are  thus  carried  out  of  danger. 

Reproduction.  —  Reproduction  in  Euglena  takes  place  by 
binary  longitudinal  division  (Fig.  22,  E).  The  nucleus  divides 
by  a  primitive  sort  of  mitosis.  The  body  begins  to  divide  at 
the  anterior  end.  The  old  flagellum  is  retained  by  one  half,  while 
a  new  flagellum  is  developed  by  the  other.  Frequently  Euglence 
become  spherical  and  secrete  a  gelatinous  covering,  called  a 
cyst.  Periods  of  drought  are  successfully  passed  while  in  the 
encysted  condition,  the  animals  becoming  active  when  water  is 
again  encountered.  Sometimes  division  takes  place  during 
encystment  (Fig.  22,  F,  G).  One  cyst  usually  produces  two 
Euglence  J  although  these  may  divide  while  still  within  the  old 


PHYLUM  PROTOZOA 


45 


cyst  wall,  making  four  in  all.  Recent  observers  have  recorded 
as  many  as  thirty-two  young  flagellated  EuglencB  which  escaped 
from  a  single  cyst. 

b.  Mastigophora  in  General 

The  Mastigophora  may  easily,  be  distinguished  from  other 
Protozoa  by  the  presence  of  one  or  more  flagella.  Four  orders 
are  usually  recognized:    (i)  Flagellata,  (2)  Choanoflagel- 

LATA,  (3)  DiNOFLAGELLATA,  (4)  CySTOFLAGELLATA. 

Order  i.  Flagellata.  —  Mastigophora  with  one  or  more 
flagella  at  the  anterior  end  of  the  body.  Examples:  Euglena 
(Fig.  22),  Mastigameba  (Fig.  24),  Chilomonas  (Fig.  25),  Uroglena 

(Fig.  26),  Volvox  (Fig.  27). 

Mastigameba  (Fig.  24)  is 

J'  of  special  interest,  since  it 


Fig.  24.  —  Mas- 
tigameba reptans,  a 
Flagellate. 


Fig.  25.  —  Chilo- 
monas, a  Flagellate. 
c.v,  contractile  vacu- 
ole; ft,  flagella;  g,  gul- 
let ;  nu,  nucleus ;  x, 
dorsal  or  upper  lip ; 
y,  ventral  or  lower  lip. 
(From  Jennings.) 


Fig.  26.  —  Uroglena  ameri- 
cana,  a  large  colonial  Flagel- 
late. (From  Bergen  and  Davis, 
adapted  after  Moore.) 


appears  to  combine  the  distinguishii>g  characteristics  of  both 
the  RmzopoDA  and  Mastigophora,  that  is,  it  possesses  pseudo- 
podia  and  also  a  distinct  flageilum.  It  is  therefore  able  to  creep 
about  on  a  solid  object  or  swim  directly  through  the  water. 

Chilomonas  (Fig.  25)  is  a  very  common  Flagellate  in  labo- 
ratory cultures.      Uroglena  (Fig.  26)  forms  spheroidal  colonies 


46 


COLLEGE  ZOOLOGY 


consisting  of  a  great  number  of  individuals  held  together  by  a 
gelatinous  matrix.  This  form  is  often  responsible  for  the  "  oily 
odor  "  of  drinking  water  caused  by  the  escape  of  small  droplets 
of  an  oil-like  substance  from  the  cells. 

Volvox  (Fig.  27)   is  a  colonial  Flagellate  found  in  fresh- 
water ponds.     It  may  consist  of  as  many  as  twelve  thousand 


Fig.  27.  —  Volvox  globator,  a  large  colonial  Flagellate.  A,  a  sexually  ripe 
colony,  showing  microgametes,  $ ,  and  macrogametes,  9 .  in  various  stages  of 
development.  B,  a  portion  of  the  edge  of  the  colony  highly  magnified,  show- 
ing three  flagellate  cells  united  by  protoplasmic  threads,  and  a  single  repro- 
ductive cell,  rp;  st,  stigma;  cv,  contractile  vacuole.  (From  Bourne,  after 
KoUiker.) 

cells.     Protoplasmic  strands  connect  each  cell  with  those  that 
surround  it  (Fig.  27  B);   physiological  continuity  is  thus  estab- 


PHYLUM   PROTOZOA 


47 


lished.  All  of  the  cells  are  not  alike,  since  some  of  them,  the  germ 
cells  (Fig.  27,  ^  and  $ )  are  able  to  produce  new  colonies,  but 
others,  called  somatic  or  body  cells,  have  no  reproductive  power. 
Some  of  the  germ  cells,  the  parthenogonidia,  grow  large,  divide 
into  many  cells,  drop  into  the  center  of  the  mother  colony,  and 
finally  escape  through  a  break  in  the  wall.  Other  germ  cells  (S) 
produce  by  division  a  great  number  of 
minute  microgametes  or  spermatozoa, 
and  still  others  grow  large,  becoming 
macrogametes  or  eggs  ($).     The   eggs 


Fig.  28.  —  Monosiga, 
a  Choanoflagellate. 
c,  collar;  c.  vac,  contrac- 
tile vacuole;  jl,  flagel- 
lum  ;  nu,  nucleus  ; 
s,  stalk.  (From  the 
Cambridge  Natural  His- 
tory, after  Kent.) 


Fig.  29.  —  Proterospongia  haeckeli,  a 
colonial  Choanoflagellate.  a,  ameboid 
cell;  b,  a  cell  dividing;  c,  cell  with  small 
collar;  z,  jelly.  (From  the  Cambridge 
Natural  History,  after  Kent.) 


are  fertilized  by  the  spermatozoa,  and,  after  a  resting  stage, 
develop  into  new  colonies. 

Order  2.  Choanoflagellata.  —  Mastigophora  with  a  con- 
tractile protoplasmic  collar  from  the  bottom  of  which  extends 
a  single  flagellum.  Examples:  Monosiga  (Fig.  28),  Protero- 
spongia (Fig.   29). 

Order  3.  Dinoflagellata.  —  Mastigophora  with  two  flagella, 
one  at  the  anterior  end,  the  other  passing  around  the  body, 
often  in  a  groove.     Examples:    Peridinium  (Fig.  30),  Ceratium. 


48 


COLLEGE   ZOOLOGY 


Order  4.     Cystoflagellata.  —  Mastigophora  with  two  flagella, 
one  resembling  a   tentacle,  the  other  lying  in  the  gullet.     Ex- 
amples :      NocHluca     (Fig.     31), 
Leptodiscus. 

Enormous  numbers  of  NocH- 
luca are  often  found  floating 
near  the  surface  of  the  sea,  giv- 
ing it  the  appearance,  as  Haeckel 


Fig.  30.  —  Peridinium 
divergens,  a  Dinoflagel- 
LATE.  a,  flagellum  of  longi- 
tudinal groove ;  b,  flagel- 
lum of  transverse  groove; 
cr.  V,  contractile  vacuole 
surrounded  by  formative 
vacuoles;  n,  nucleus. 
(From  the  Cambridge  Nat- 
ural History,  after  Schiitt.) 


Fig.  31. — Noctilucamili- 
aris,  a  Cystoflagellate. 
(From  Weysse,  after  Cien- 
kowski.) 


says,  of  "tomato  soup."    At  night  they  are  phosphorescent, 
emitting  a  bluish  or  greenish  light. 


3.   Class  III.    Sporozoa 

a.  Monocystis 

Monocystis  (Fig.  32)  is  a  Sporozoon  easily  obtained  for  study 
in  the  laboratory,  since  it  is  a  parasite  in  the  seminal  vesicles  of 
the  common  earthworm.  It  is  about  yj^^  inch  long.  No 
locomotor  organs  of  any  kind  are  present.  The  life  history  of 
Monocystis  is  shown  in  Figure  32,  and  may  be  described  briefly 
as  follows. 

The  animals  are  in  some  unknown  way  transferred  from  one 
earthworm  to  another  as  spores  (Fig.  32,   K),  each  containing 


ep:       H 


Fig.  32.  —  Monocystis,  a  Sporozoon  parasitic  in  the  seminal  vesicle  of  the 
earthworm.  A,  the  eight  sporozoites  {spz)  escaping  from  the  sporocyst.  B, 
a  young  trophozoite  {tr)  among  the  sperm-mother  cells  {sp)  of  the  earthworm. 
C,  a  free  individual  with  a  few  withered  sperm  cells  adhering  to  it.  D,  a  mature 
individual  attached  to  the  sperm-funnel  {sf)  of  the  earthworm.  E,  two  mature 
individuals  joined  side  by  side.  F,  two  individuals  have  formed  a  cyst;  en, 
endocyst;  e^,  epicyst;  «,  nucleus.  G,.  gametes  (gam)  formed  by  one  individual 
within  the  cyst.  H,  conjugation  of  gametes  to  form  zygotes  (zy).  I,  zygotes 
that  have  secreted  spore  coat  or  sporocysts  and  have  become  sporoblasts  {sp). 
J,  a  single  sporoblast  in  which  the  nucleus  has  divided,  forming  eight  daughter 
nuclei.  K,  a  fully  developed  sporocyst  containing  eight  sporozoites  (spz). 
(From  Bourne,  after  Cuenot  and  Bourne.) 


50  COLLEGE  ZOOLOGY 

eight  elongated  bodies  called  sporozoUes  (K,  A,  spz).  Each 
sporozoite  penetrates  a  bundle  of  sperm  mother  cells  {B,  sp)  of 
the  earthworm,  and  is  then  termed  a  trophozoite  {B,  tr).  Here  it 
lives  at  the  expense  of  the  cells  among  which  it  lies.  The 
spermatozoa  of  the  earthworm,  which  are  deprived  of  nourish- 
ment by  the  parasite,  slowly  shrivel  up  (C),  finally  becoming 
tiny  filaments  on  the  surface  of  the  trophozoite  {D). 

When  this  stage  is  reached,  two  trophozoites  come  together  {E) 
and  are  surrounded  by  a  common  two-layered  cyst  wall  {F,  ep, 
en).  Each  then  divides,  producing  a  number  of  small  cells  called 
gametes  (G).  The  gametes  unite  in  pairs  (H)  to  form  zygotes 
(zy).  It  is  probable  that  the  gametes  produced  by  one  of  the 
trophozoites  do  not  fuse  with  each  other,  but  with  gametes 
produced  by  the  other  trophozoite  enclosed  in  the  cyst.  Each 
zygote  becomes  lemon-shaped,  and  secretes  a  thin  hard  wall  about 
itself.  It  is  now  known  as  a  sporoblast  (/).  The  nucleus  of  the 
sporoblast  divides  successively  into  two,  four,  and  finally  eight 
daughter  nuclei  (/);  each  of  these,  together  with  a  portion  of 
the  cytoplasm,  becomes  a  sporozoite  {K,  A,  spz). 

b.  Plasmodium  vivax 

One  of  the  best  known  of  all  the  Sporozoa  is  Plasmodium 
vivax,  which  causes  malarial  fever.  This  minute  animal  was 
discovered  in  the  blood  of  malaria  patients  by  a  French  military 
doctor,  Laveran.  It  was  suggested  by  this  investigator,  in 
1 89 1,  that  the  parasite  is  probably  transmitted  from  man  to  man 
by  some  blood-sucking  insects,  and  this  hypothesis  was  proved 
to  be  correct  by  the  work  of  Major  Ross  in  1899.  Not  only  was 
it  demonstrated  that  malaria  is  spread  by  insects,  but  it  was 
proved  that  human  beings  can  only  become  infected  by  the  bite 
of  a  diseased  mosquito  belonging  to  the  genus  Anopheles.  The 
two  most  common  genera  of  mosquitoes  are  Culex  and  Ano- 
pheles. One  of  the  easiest  methods  of  distinguishing  one  from 
the  other  is  by  observing  their  position  when  at  rest.  It  will  be 
found  that  the  harmless  Culex  holds  its  abdomen  approximately 


PHYLUM   PROTOZOA  5 1 

parallel  to  the  surface  on  which  it  alights,  whereas  the  abdomen 
of  Anopheles  is  held  at  an  angle. 

There  are  three  well  known"  types  of  malaria;  these  may  be 
recognized  by  the  intervals  between  successive  chills,  (i) 
Tertian  fever,  caused  by  Plasmodium  vivax,  is  characterized  by 
an  attack  every  forty-eight  hours;  (2)  quartan  fever,  caused  by 
Plasmodium  malarice,  with  an  attack  every  seventy-two  hours, 
and  (3)  estivo-autumnal  or  pernicious  fever,  caused  by  Plas- 
modium falciparum,  produces  attacks  daily,  or  more  or  less  con- 
stant fever.  The  life  histories  of  these  three  species  of  Plas- 
modium differ  very  shghtly  one  from  another. 

Tertian  fever  is  transmitted  by  diseased  female  mosquitoes 
only.  The  mouth  parts  of  these  insects  are  adapted  for  piercing. 
When  they  have  been  thrust  into  the  skin  of  the  victim,  a  little 
saliva  is  forced  into  the  wound.  This  saliva  contains  a  weak 
poison,  which  is  supposed  to  prevent  the  coagulation  of  the  blood 
and  thus  the  clogging  of  the  puncture.  Blood  is  sucked  up  by 
the  mouth  parts  into  the  alimentary  canal  of  the  mosquito; 
this  process  occupies  from  two  to  three  and  a  half  minutes. 
With  the  saliva  a  number  of  parasites,  which  were  stored  in  the 
salivary  glands  of  the  insect,  find  their  way  into  the  wound. 
The  human  blood  corpuscles  are  immediately  entered  by  the 
parasites,  and  their  contents  slowly  consumed.  Finally  the 
blood  corpuscle  breaks  down,  and  the  spores,  which  were  formed 
within  it  by  the  parasite,  escape. 

The  malaria  parasite  multiplies  very  rapidly,  and  the  "  chill  " 
so  characteristic  of  the  disease  results  either  from  the  simul- 
taneous destruction  of  great  numbers  of  blood  corpuscles  or 
from  the  Hberation  of  a  poison  produced  by  the  parasites. 
When  a  mosquito  bites  a  malaria  patient,  it  sucks  up  some 
of  the  parasites  with  the  blood.  These  parasites  pass  through 
part  of  their  life  history  within  the  alimentary  canal  and 
body  cavities  of  the  insect,  and,  after  a  period  of  multiplica- 
tion, make  their  way  into  the  salivary  glands.  They  are  then 
ready  to  be  injected  into  the  next  human  being  the  mosquito 


52  COLLEGE  ZOOLOGY 

bites.  Quinine  is  the  remedy  commonly  used  against  the 
malarial  parasite.  It  acts  directly  upon  the  younger  stages 
of  the  organism,  causing  their  death. 

c.   Sporozoa  in  General 

The  Sporozoa  are  Protozoa  without  motile  organs.  They 
are  parasitic  in  Metazoa.  Reproduction  is  mainly  by  spore 
formation.  The  following  classification  is  simplified  from  Min- 
chin's  account  in  Lankester's  Treatise  on  Zoology,  Part  I. 

Subclass  i  .  Telosporidia.  —  Sporozoa  in  which  the  life  of 
the  individual  ends  in  spore  formation. 

Order  i.  Gregarinida. — Telosporidia  possessing  a  firm 
pellicle  and  complex  ectosarc;  intracellular  during  the  early 
stages  of  the  life  cycle,  later  free  in  the  body  cavities  of  inverte- 
brates.    Examples:  Monocystis  (Fig.  32),  Porospora,  Gregarina. 

Monocyslis  (Fig.  32)  may  be  found  in  the  seminal  vesicles  of 
almost  every  earthworm;  Gregarina  is  a  common  parasite  of  the 
cockroach;  and  Porospora  gigantea,  which  reaches  a  length  of 
two-thirds  of  an  inch,  inhabits  the  alimentary  canal  of  the  lob- 
ster. 

Order  2.  Coccidiidea. — Telosporidia  simple  in  structure; 
trophozoite  is  a  minute  intracellular •  parasite.  Example:  Coc- 
cidium. 

Members  of  this  order  are  sometimes  found  in  the  liver  and 
intestine  of  man  and  other  vertebrates,  and  in  Arthropoda  and 

MOLLUSCA. 

Order  3.  Haemosporidia.  —  Telosporidia  parasitic  in  the 
blood  of  vertebrates.  •  Example:    Plasmodium  (p.  50). 

Subclass  2.  Neosporidia.  —  Sporozoa  which  give  rise  to 
spores  at  intervals  during  active  life. 

Order  i.  Myxosporidia.  —  Neosporidia  with  ameboid  inter- 
cellular trophozoite.     Example:   Nosema. 

The  Myxosporidia  are  parasitic  especially  in  Arthropoda 
and  fish,  frequently  causing  serious  epidemics  in  aquaria. 
Nosema  bombycis  produces  the  silkworm  disease,  pebrine. 


PHYLUM  PROTOZOA 


S3 


Order  2.  Sarcosporidia.  —  Neosporidia  usually  parasitic  in 
the  muscles  of  vertebrates.     Example:  Sarcocystis. 

The  most  common  Sarcosporidia  are  Sarcocystis  miescheri- 
ana  in  the  muscle  of  the  pig,  S.  muris  in  that  of  the  mouse,  S, 
lindemanniy  rarely  occurring  in  the  muscles  of  human  beings. 


4.  Class  IV.    Infusoria 


a.   Paramecium  caudatum 

Paramecia  are  unicellu- 
lar animals  visible  to  the 
naked  eye  if  a  proper  back- 
ground is  provided.  They 
are  found  in  fresh  water, 
and  usually  appear  in  cul- 
tures prepared  for  Ameba 
as  described  on  page  28. 

Anatomy.  — Paramecium 
(Fig.  33)  is  a  cigar-shaped 
animal  with  a  depression 
called  the  oral  groove  (o.g.) 
extending  from  the  forward 
end  obliquely  backward, 
ending  just  posterior  to 
the  middle  of  the  body. 
The  mouth  (m.)  is  situated 
near  the  end  of  the  oral 
groove.  Endosarc  {en.) 
and  ectosarc  (ec.)  occur  in 
Paramecium  as  in  Ameba. 
Covering  the  surface  is  an 
additional  membrane,  the 
pellicle  (p.)  or  cuticle;  this 
can  easily  be  seen  if  a 
drop  or  two  of  35  per  cent 


m^ 


Fig.  33. — Paramecium  viewed  from  the 
oral  surface.  L,  left  side.  R,  right  side. 
an,  anus;  ec,  ectosarc;  en,  endosarc;  f.v,  food 
vacuoles;  g,  gullet;  m,  mouth;  ma,  macro- 
nucleus;  mi,  micro'nucleus;  o.  g,  oral  groove; 
p,  pellicle;  tr,  trichocyst  layer.  The  arrows 
show  the  direction  of  movement  of  the  food 
vacuoles.     (From  Jennings.) 


54 


COLLEGE  ZOOLOGY 


alcohol  is  added  to  a  drop  of  water  containing  specimens.     The 
pellicle  will  then  be  raised  as  a  blister,  and  will  be  seen  to 

consist  of  many  hexagonal  areas 
which  produce  striations  on  the 
surface. 

The  motile  organs  are  thin 
thread-like  cilia,  one  of  which  pro- 
jects from  the  center  of  each  hex- 
agonal area  of  the  cuticle.  The 
beating  of  the  cilia  propels  the 
animal  forward  or  backward,  and 
draws  food  particles  into  the 
mouth. 

Just  beneath  the  pellicle  is  a 
layer  of  spindle-shaped  cavities  in 
the  ectoplasm  filled  with  a  semi-fluid  substance.  These  are 
called  trichocysts  (tr.) ,  and  are  probably  weapons  of  offense  and 
defense.  Under  certain  conditions  the  trichocysts  may  be  ex- 
ploded, for  example  when  a  little  acetic  acid  is  added  to  the 
water,  and  long  threads  are  discharged. 
Figure  34  shows  a  Paramecium  repelling 
the  attack  of  another  Protozoon  by  the 
explosion  of  its  trichocysts. 

Two  cqntrqftik  vacuoles  are  present, 
one  near  either  end  of  the  body.  Each 
communicates  with  a  large  portion  of  the 
body  by  means  of  a  system  of  radiating 


Fig.  34.  —  Paramecium  defend 
ing  itself  from  an  attack  by  i 
Protozoon,  Didinium.  The  trich 
ocysts  are  discharged  and  me 
chanically  force  the  enemy  away 
(From  Mast  in  Biol.  Bui.) 


canals,  six  to  ten   in  number. 


Fig.  35.  —  Paramecium 
These  swimming  in  a  solution  of 
India  ink,  showing  the  dis- 
charge of  the  contractile 
vacuoles  to  the  outside. 
(From  Dahlgren  and  Kep- 
ner,  after  Jennings.) 


canals  collect  fluid  from  the  surround- 
ing protoplasm  and  pour  it  into  the 
vacuole.  The  vacuoles  contract  alter- 
nately   at    intervals    of    about    ten    to 

twenty  seconds.  Their  fluid  contents  are  discharged  to  the 
outside  (Fig.  35).  As  in  Ameba,  they  act  as  organs  of  excretion 
and  respiration. 


PHYLUM   PROTOZOA 


55 


Metabolism.  —  The  food  of  Paramecium  consists  principally 

of  Bacteria  and  minute  Protozoa.    The  cilia  in  the  oral  groove 

(Fig.  33,  o.g.)  create  a  current  of 

water    toward    the    mouth    {m.). 

Food  particles  are  forced  down  the 

gullet  {g.)  by  a  row  of  cilia  which^ 

have  fused  side  by  side,  forming 

an  undulating  membrane.     At  the 

end  of  the  gullet  sl  food  vacuole  (f.v.) 

is  produced;  this  when  fully  formed 

separates   from   the   gullet  and  is 

swept  away  by  the  rotary  stream- 
ing movement  of  the  endoplasm, 

known   as   cyclosis.      This   carries 

the  food  vacuole  around  a  definite 

course,  as  shown  by  the  arrows  in 

Figure  33.     Digestion  occurs  within 

the  food  vacuole.     Undigested  par- 
ticles  are   cast   out   at  a   definite 

anal  spot  (Fig.  33,  an.)^  which  can 

only  be  seen  when  the  faeces  are 

/    voided.     The   processes   of   diges- 

,'     tion,  absorption,   assimilation,  ex- 

)      cretion,  and  respiration  are  similar 

to  those  described  for  Ameha. 
N^^  Behavior.  —  Locomotion.  —  If 

confined  in  close  quarters,   Para- 
mecium exhibits  elasticity^  and  can 

squirm    through    small    openings; 

but  w^hen  in  a  free  field  it  swims 

by  means  of  its  cilia.     These  are 

inclined   backward  and  obliquely, 

so  that  the  body  is  rotated  in  its 

long  axis  over  to  the  left  as  well 

as  propelled  forward  (Fig.  36). 


56  COLLEGE   ZOOLOGY 

"  The  cilia  in  the  oral  groove  beat  more  effectively  than  those 
elsewhere.  The  result  is  to  turn  the  anterior  end  continually 
away  from  the  oral  side,  just  as  happens  in  a  boat  that  is  rowed 
on  one  side  more  strongly  than  on  the  other.  As  a  result  the 
animal  would  swim  in  circles,  turning  continually  toward  the 
aboral  side,  but  for  the  fact  that  it  rotates  on  its  long  axis. 
Through  the  rotation  the  forward  movement  and  the  swerving 
to  one  side  are  combined  to  produce  a  spiral  course.  The  swerv- 
ing when  the  oral  side  is  to  the  left,  is  to  the  right;  when  the  oral 
side  is  above,  the  body  swerves  downward;  when  the  oral  side 
is  to  the  right,  the  body  swerves  to  the  left,  etc.  Hence  the 
swerving  in  any  given  direction  is  compensated  by  an  equal 
swerving  in  the  opposite  direction;  the  resultant  is  a  spiral  path 
having  a  straight  axis  "  (Fig.  36). 

Rotation  is  thus  effective  in  enabling  an  unsymmetrical 
animal  to  swim  in  a  straight  course  through  a  medium  which 
allows  deviations  to  right  or  left,  and  up  or  down. 

Reactions  to  Stimuli.  —  Paramecium  responds  to  stimuli 
either  negatively  or  positively.     The  negative  response  is  known 


Fig.  37.  —  Diagram  of  the  avoiding  reaction  of  Paramecium.  A  is  a  solid 
object  or  other  source  of  stimulation.  i-6,  successive  positions  occupied 
by  the  animal.     (The  rotation  on  the  long  axis  is  not  shown.)    (From  Jennings.) 

as  the  "  avoiding  reaction  "  (Fig.  37) ;  it  takes  place  in  the  follow- 
ing manner.     When  a  Paramecium  receives  an  injurious  stimulus 


PHYLUM    PROTOZOA  57 

at  its  anterior  end,  it  reverses  its  cilia  and  swims  backward  for 
a  short  distance  out  of  the  region  of  stimulation;  then  its  rota- 
tion decreases  in  rapidity  and  it  swerves  toward  the  aboral  side 
more  strongly  than  under  normal  conditions.  Its  posterior 
end  then  becomes  a  sort  of  pivot  upon  which  the  animal  swings 
about  in  a  circle  (Fig.  37,  j-5).  During  this  revolution  samples 
of  the  surrounding  medium  are  brought  into  the  oral  groove. 
When  a  sample  no  longer  contains  the  stimulus,  the  cilia  resume 
their  normal  beating,  and  the  animal  moves  forward  again.  If 
this  once  more  brings  it  into  the  region  of 
the  stimulus,  the  avoiding  reaction  is  re- 
peated; this  goes  on  as  long  as  the  animal 
receives  the  stimulus.  The  repetition  of 
the  avoiding  reaction  is  very  well  shown 
when  Paramecium  enters  a  drop  of  3^  per 
cent  acetic  acid.  In  attempting  to  get  out 
of  the  drop  the  surrounding  water  is  en-     ,   Fig.  38.  — Path  fol- 

*  ^  ^  ^  ^         ^        lowed  by  a  single  Pa- 

countered;   to  this  the  avoiding  reaction  is     ramecium   in  a  drop 
given  and  a  new  direction  is  taken  within     °!  ^^^f-    (From  Jen- 

*=*  nings.) 

the  acid,  which  of  course  leads  to  the  water 
and  another  negative  reaction.     The  accompanying  Figure  ^8 
shows  part  of  the  pathway  made  by  a  single  Paramecium  under 
these  conditions. 

Paramecium  responds  positively  under  certain  conditions. 
Often  it  comes  to  rest  against  an  object,  positive  thigmotropism. 
When  subjected  to  chemical  substances  or  heat,  it  swims  about 
in  all  directions,  giving  the  avoiding  reaction  until  it  succeeds  in 
getting  into  a  suitable  environment.  This  is  the  method  of  trial 
and  error,  that  is,  the  animal  tries  all  directions  until  the  one  is 
discovered  which  allows  it  to  escape  from  the  region  of  un- 
favorable stimulation.  "  For  each  chemical  there  is  a  certain 
optimum  concentration  in  which  the  Paramecia  are  not  caused 
to  react."  There  is  also  an  optimum  temperature,  which  lies, 
under  ordinary  conditions,  between  24°  and  28°  C. 

Gravity  stimulates   Paramecium  in  some  unknown  way  to 


58  COLLEGE  ZOOLOGY 

orient  itself  with  the  forward  end  pointing  upward,  so  that  if  a 
number  are  equally  distributed  in  a  test  tube  of  water,  they  will 
gradually  find  their  way  to  the  top.  In  running  water,  Para- 
mecia  swim  upstream,  probably  because  the  current  would  inter- 
fere with  the  beating  of  the  cilia  if  any  other  direction  were 
taken.  The  electric  current  also  affects  the  beating  of  the  cilia 
and  causes  certain  definite  movements. 

Frequently  Paramecium  may  be  stimulated  in  more  than  one 
way  at  the  same  time.  For  example,  a  specimen  which  is  in 
contact  with  a  solid  is  acted  upon  by  gravity,  and  may  be  acted 
upon  by  chemicals,  heat,  currents  of  water,  and  other  stimuli. 
It  has  been  found  that  gravity  always  gives  way  to  other  stimuli, 
and  that  if  more  than  one  other  factor  is  at  work  the  one  first 
in  the  field  exerts  the  greater  influence. 

Both  the  spontaneous  activities,  such  as  swimming,  and  re- 
actions due  to  external  stimuli,  are  due  to  changes  in  the  internal 
condition  of  the  animal.  The  physiological  condition  of  Parame- 
cium, therefore,  determines  the  character  of  its  response.  This 
physiological  state  is  a  dynamic  condition,  changing  continually 
with  the  processes  of  metaboUsm  going  on  within  the  living 
substance  of  the  animal.  Thus  one  physiological  state  resolves 
itself  into  another;  this  "  becomes  easier  and  more  rapid  after 
it  has  taken  place  a  number  of  times,"  giving  us  grounds  for  the 
belief  that  stimuli  and  reactions  have  a  distinct  effect  upon 
succeeding  responses. 

"  We  may  sum  up  the  external  factors  that  produce  or  deter- 
mine react* ons  as  follows:  (i)  The  organism  may  react  to  a 
change,  even  though  neither  beneficial  nor  injurious.  (2)  Any- 
thing that  tends  to  interfere  with  the  normal  current  of  life 
activities  produces   reactions   of   a   certain   sort   ('  negative  ')• 

(3)  Any  change  that  tends  to  restore  or  favor  the  normal  life 
processes  may  produce  reactions  of  a  different  sort  ('  positive  ')• 

(4)  Changes  that  in  themselves  neither  interfere  with  nor  assist 
the  normal  stream  of  life  processes  may  produce  negative  or 
positive  reactions,  according  as  they  are  usually  followed  by 


PHYLUM   PROTOZOA 


59 


changes  that  are  injurious  or  beneficial.  (5)  Whether  a  given 
change  shall  produce  reaction  or  not  often  depends  on  the  com- 
pleteness or  incompleteness  of  the  performance  of  the  metabolic 
processes  of  the  organism  under  the  existing  conditions.  This 
makes  the  behavior  fundamentally  regulatory." 
"  Reproduction.  —  Paramecium  reproduces  only  by  simple 
Unary  division.  This  process  is  interrupted  occasionally  by 
a  temporary  union  {conjugation)  of  two  indi- 
viduals and  a  subsequent  mutual  fertilization. 
"  Binary  fission.  —  In  binary  fission  the 
animal  divides  transversely  (Fig.  39).  Both 
the  macronucleus  (Fig.  39,  N)  and  micro- 
nucleus  {n)  divide,  forming  daughter  nuclei. 
A  new  gullet  {0^)  is  budded  off  from  the  old 
gullet  {0),  and  two  new  contractile  vacuoles 
arise.  The  animal  is  then  divided  into  two 
by  a  constriction.  The  entire  process  occupies 
from  about  half  an  hour  to  two  hours.  The 
daughter  Paramecia  grow  rapidly  and  divide 
again  at  the  end  of  twenty-four  hours  or  even 
sooner,  depending  on  the  temperature,  food, 
and  other  external  conditions.  It  has  been  fig.  ^q,  —  Para- 
estimated  that  one  Paramecium  may  be  re-   »««'^»«w  dividing  by 

•1  1      r  1        •  r      ^r,  binary     fission.       N, 

sponsible   for   the   production   of    268,000,000    j^S      macronucleus  ; 

offspring  in  one  month.  «>  '^z  micronucleus ; 

^  ,  ,.  .  ,         .    .  .      0,    o\    mouth.       The 

Conjugation.  —  The  conditions  that  imti-  Paramecium    figured 
ate  conjugation  are  not  yet  known,  but  the  ^^^  ^wo  micronuclei. 

,.  ,  ,  ,  .         r   11       (From  Sedgwick,  after 

complicated  stages  have  been  quite  fully  Hertwig.) 
worked  out.  When  two  Paramecia,  which 
are  ready  to  conjugate,  come  together,  they  remain  attached  to 
each  other  because  of  the  adhesive  state  of  the  external  proto- 
plasm. The  ventral  surfaces  of  the  two  animals  are  opposed, 
and  a  protoplasmic  bridge  is  constructed  between  them.  As 
soon  as  this  union  is  effected,  the  nuclei  pass  through  a  series 
of  stages  which  have  been  likened  to  the  maturation  processes 


6o 


COLLEGE  ZOOLOGY 


of  metazoan  eggs  (Chap.  Ill,  p.  8i).  Reference  to  Figure  40 
will  help  to  make  clear  the  following  description.  The  micro- 
nucleus  moves  from  its  normal  position  in  a  concavity  of  the 


Fig.  40.  —  Paramecia  conjugating,  a-q,  stages  in  the  nuclei  during  con- 
jugation and  the  subsequent  divisions  of  the  conjugants  during  the  period  of 
nuclear  reconstruction.  The  original  macronuclei  have  been  omitted  except 
in  stage  a.     (After  Calkins  and  Cull.) 


PHYLUM   PROTOZOA 


6l 


macronucleus  (Fig.  33,  mi.),  grows  larger,  then  lengthens, 
forming  a  spindle  (Fig.  40,  a),  and  subsequently  divides  into 
two  (b).  These  immediately  divide  again  without  the  inter- 
vention of  a  resting  stage.  The  resultant  four  nuclei  (c)  have 
been  compared  to  the  four  sper- 
matozoa produced  by  a  primary 
spermatocyte  or  to  an  egg  with 
its  polar  bodies,  and  the  divi- 
sions are  considered  as  the  first 
and  second  maturation  mitoses 
(see  p.  81).  Three  of  the  four 
nuclei  degenerate  (d),  the  fourth 
divides  again.  During  this  divi- 
sion the  granules  of  chromatin 
contained  in  the  nuclei  separate 
into  two  groups,  one  smaller 
(Fig.  41,  A,  m.n.)  than  the 
other  (Fig.  41,  ^,  f.n.).  The 
smaller  nucleus  might  be  con- 
sidered comparable  to  the  male 
nucleus,  the  other  to  the  female. 
The  male  nucleus  migrates  across 
the  protoplasmic  bridge  between 

the  two  animals  (Fig.  40,/)  and   which  resuUs  in"  the  prVductio'n 
unites  with  the  female  nucleus  of  ^^^^f,  ^^^^^^   nucleus   (/«)   and  a 

smaller  male  nucleus   {m.n).      B,  the 

the  Other  COnjUgant  (Fig.  40,  g;    fusion  of  the  male   nucleus  (m.n)  of 

Fig.    41,    B),    forming    a    fusion    one  conjugant  with  the  female  nucleus 

^     ^   '        ^'  '^  (/.«)  of  the  other  conjugant.     (From 

nucleus    (Fig.    40,    h).      Thus    is    Calkins  and  Cull  in  ^rcAii;/.  Pro/w/.) 

fertilization  effected. 

The  conjugants  separate  soon  after  fertilization  (Fig.  40,  g). 
The  macronucleus,  which  up  to  this  time  has  remained  at  rest, 
now  assumes  a  vermiform  shape,  breaks  up  into  small  segments, 
and  then  dissolves.  Shortly  after  separation  the  fusion  nucleus 
of  each  conjugant  divides  by  mitosis  into  two  (i),  these  two  into 
four  (J),  and  these  four  into  eight  nuclei  equal  in  size  (k).     Four 


Fig.  41.  —  Two  views  of  the  micro- 
nuclei  during  the  conjugation  of 
Paramecium.  A,  the  spindle  formed 
during  the  division  of  the  micronucleus 


62  COLLEGE  ZOOLOGY 

of  these  increase  in  size  and  develop  into  macronuclei  (/);  the 
other  four  remain  micronuclei.  The  whole  animal  then  divides 
by  binary  fission  {m,  n),  each  daughter  cell  securing  two  of  the 
macronuclei  and  two  micronuclei  {o).  Another  binary  division 
(/>)  results  in  four  cells  each  with  one  macronucleus  and  one 
micronucleus  {q).  An  indefinite  number  of  generations  are 
produced  by  the  transverse  division  of  the  four  daughter  cells 
resulting  from  each  conjugant. 

The  significance  of  conjugation  cannot  be  definitely  stated. 
Some  investigators  believe  that  Paramecium  passes  through  a 
life  cycle  containing  three  distinct  stages.  The  period  of  (i) 
youth  is  characterized  by  rapid  cell  multiplication  and  growth; 
(2)  maturity  by  less  frequent  cell  division,  sexual  maturity,  and 
the  cessation  of  growth;  and  (3)  old  age  by  degeneration  and 
natural  death.  Death  is  avoided  by  conjugation,  which  rejuve- 
nates the  senescent  animals. 

Jennings  has  shown  that  some  Paramecia  conjugate  more 
often  than  others,  and  Woodruff  has  succeeded  in  carrying  a  cul- 
ture through  a  period  of  over  four  and  one  half  years.  During 
this  time  there  were  two  thousand  seven  hundred  and  five 
generations.  These  facts  "  weaken  the  theory  that  conjugation 
is  to  be  considered  the  result  of  senile  degeneration  at  the  end  of 
the  life  cycle,"  and  show  that  this  Protozoon  "'  has  unlimited 
power  of  reproduction  without  conjugation  or  artificial  stimula- 
tion "  if  given  a  favorable  environment. 

b.  Infusoria  in  General 

The  Infusoria  are  Protozoa  with  cilia  which  serve  as  loco- 
motor organs  and  for  procuring  food.  Paramecium  is  a  typical 
member  of  the  class.     There  are  two  subclasses,  (i)  Ciliata  and 

(2)  SUCTORTA. 

Subclass  i.  Ciliata.  —  Infusoria  with  cilia  in  the  adult 
stage,  a  mouth,  and  usually  undulating  membranes  or  cirri. 
Many  ciliates  are  confined  to  fresh  water,  others  occur  either  in 
fresh  or  salt  water,  and  still  others  are  parasitic  in  Metazoa. 


PITi'LUM   PROTOZOA 


63 


There  are  four  orders:   (i)  Holotricha,  (2)  Heterotricha, 
(3)  Hypotricha,  (4)  Peritricha. 

Order  i.  Holotricha  (Figs,  t,;^  and  42).  —  Ciliata  with  cilia 
all  over  the  body  and  of  approximately  equal  length  and  thick- 
ness. Examples:  -Paramecium  (Fig.  33),  Coleps  (Fig.  42,  A), 
Loxophyllum  (Fig.  42,  B),  Colpodq,  (Fig.  42,  C),  Opalina  (Fig. 

The  HoLOTRiCHA'^ie  probably  the  most  primitive  Infusoria. 
Paramecium  caudatum  is>the  best  known  species.     Members  of 


B  C 

-Infusoria  of  the  order  Holotricha.  A,  Coleps  hirtus.  B,  Loxo- 
phyllum rostratum.  C,  Colpoda  cucullulus.  D,  Opalina  ranarum;  a,  macro- 
nuclei.     (A,  B,  C,  from  Conn;    D  from  Lankester,  after  Zeller.) 


the  following  genera  are  frequently  found  in  fresh- water  cultures: 
Coleps  (Fig.  42,  A),  Loxophyllum  (Fig.  42,  B),  and  Colpoda 
(Fig.  42,  C).  Opalina  ranarum  (Fig.  42,  D)  is  a  large  multi- 
nucleate species  living  in  the  intestine  of  the  frog.  It  has  no 
mouth,  but  absorbs  digested  foods  through  the  surface. 

Order  2.  Heterotricha  (Fig.  43,  A).  —  Ciliata  whose  cilia 
cover  the  entire  body,  but  are  larger  and  stronger  about  the 
mouth  opening  than  elsewhere.  This  adoral  ciliated  spiral  con- 
sists of  rows  of  cilia  fused  into  membranelles  and  leads  into  the 
mouth.  Examples:  Spirostomum,  Bursaria,  and  Stentor  (Fig. 
43,  A). 


64 


COLLEGE   ZOOLOGY 


Stentor  (Fig.  43,  A)  may  be  either  fixed  or  free  swimming. 
It  is   trumpet-shaped  when   attached   and  pear-shaped  when 
swimming.     The  cuticle  is  striated  and   just   beneath   it   are 
A  B 


c.vtte 


mffJtu, 


Fig.  43.  —  Infusoria.  A,  Stentor  polymorphus  of  the  order  Heterotricha. 
B,  Stylonychia  mytilus  of  the  order  Hypotricha.  C,  Vorticella  of  the  order 
Peritricha.  D,  Podophyra  of  the  subclass  Suctoria.  c.vac,  contractile 
vacuole ;  mg.nu,  macronucleus ;  mi.nu,  micronucleus ;  /,  disc ;  2,  mouth; 
3,  peristomial  groove;  4,  vibratile  membrane  in  mouth;  5,  ectoplasm;  6,  endo- 
plasm  ;  7,  food  vacuoles  ;  8,  pharynx  showing  formation  of  food  vacuoles  ; 
Q,  contractile  vacuoles;  10,  permanent  receptacle  into  which  contractile  vacuole 
opens;  11,  micronucleus;  12,  nucleus;  13,  contractile  fibrils  running  into 
muscle  in  stalk;  14,  stalk  contracted  (the  axial  fiber  should  touch  the  cuticle  in 
places).  (A  and  B,  from  Weysse,  after  Kent;  C,  from  Shipley  and  MacBride; 
D,  from  Parker  and  Haswell.) 

muscle  fibers  (myonemes).    The  nucleus  is  ellipsoidal,  or  like 
a  row  of  beads. 

Order  3.  Hypotricha  (Fig.  43,  B).  —  Ciliata  with  a  flattened 
body  and  dorsal  and  ventral  surfaces.     The  dorsal  surface  is  free 


PHYLUM  PROTOZOA  65 

from  cilia,  but  spines  may  be  present.  The  ventral  surface  is 
provided  with  longitudinal  rows  of  cilia  and  also  spines  and 
hooked  cirri,  which  are  used  as  locomotor  organs  in  creeping 
about.  The  cilia  around  the  oral  groove  aid  in  swimming  as 
well-  as  in  food  taking.  There  is  a  macronucleus,  often  divided, 
and  two  or  four  micronuclei.  ^Examples:  Oxytrichay  Stylo- 
nychia.  A  side  view  of  a  creeping  Stylonychia  is  shown  in 
Figure  43,  B. 

Order  4.  Peritricha  (Fig.  43,  C).  —  Ciliata  with  an  adoral 
ciliated  spiral,  the  rest  of  the  body  is  without  cilia,  except  in  a 
few  species  where  a  circlet  of  cilia  occurs  near  the  aboral  end. 
Examples:    Vorticella  (Fig.  43,   C),    Carchesium,  Zoothamnium, 

The  common  members  of  this  order  are  bell-shaped  and  at- 
tached by  a  contractile  stalk.  Certain  species  are  solitary 
(Vorticella,  Fig.  43,  C),  others  form  tree-like  colonies  (Car- 
chesium),  and  still  others  are  colonial  but  with  an  enveloping 
mass  of  jelly  {Zoothamnium).  The  anatomy  of  Vorticella  is 
shown  in  Figure  43,  C.  The  stalk  contains  a  winding  fiber  com- 
posed of  myoneme  fibrils;  this  fiber,  on  contracting,  draws  the 
stalk  into  a  shape  like  a  coil  spring. 

Subclass  2.  Suctoria.  —  Infusoria  without  cilia  in  the 
adult  stage.  No  locomotor  organs  are  present  and  the  animals 
are  attached  either  directly  or  by  a  stalk.  No  oral  groove  nor 
mouth  occurs,  but  a  number  of  tubelike  tentacles  extend  out 
through  the  cuticle.  Examples:  Podophyra  (Fig.  43,  D), 
Sphcerophyra. 

Ciliates  are  captured  by  these  tentacles  and  their  substance  is 
sucked  by  them  into  the  body.  Both  fresh-water  and  marine 
species  are  known.  Podophyra  (Fig.  43,  D)  is  a  well-known 
fresh- water  form.    Sphcerophyra  is  parasitic  in  other  Infusoria. 

5.   Protozoa  in  General 

Protozoa  may  be  defined  as  unicellular  animals  which  in 
many  cases  form  colonies.  An  examination  of  the  t5^es  dis- 
cussed in  the  preceding  pages  will  show  that  the  Protozoa  differ 


66  COLLEGE  ZOOLOGY 

one  from  another  in  structure,  physiology,  and  reproduction. 
These  differences  are  briefly  reviewed  in  the  following  para- 
graphs. 

Morphology.  —  Protozoa  vary  in  size  from  the  minute  blood 
parasites,  such  as  Plasmodium  which  causes  malaria,  to  the  huge 
gregarine,  Porospora  gigantea,  which  lives  in  the  alimentary 
canal  of  the  lobster  and  may  be  two-thirds  of  an  inch  long. 
Most  of  them  are  invisible  to  the  naked  eye,  and  a  few  are 
invisible  even  with  the  highest  powers  of  the  microscope.  For 
example,  the  organism  which  is  supposed  to  cause  yellow  fever 
is  known  only  by  its  effects  upon  human  beings,  since  it  has 
never  been  seen. 

The  shapes  of  Protozoa  are  likewise  extremely  varied. 
Ameba  has  no  definite  shape;  many  species  are  globular  with 
radiating  projections  (Heliozoa,  Fig.  i8;  Radiolaria,  Fig.  19); 
Euglena  (Fig.  22)  is  spindle-shaped;  Paramecium  (Fig.  33)  re- 
sembles a  slipper;  Vorticella  (Fig.  43,  C),  a  bell;  Stentor  (Fig.  43, 
A),  2i  trumpet;  some  like  Stylonychia  (Fig.  43,  B)  have  definite 
dorsal  and  ventral  surfaces;  in  fact,  almost  every  conceivable 
shape  seems  to  occur  in  this  group. 

Most  of  the  Protozoa  are  either  faintly  colored  or  entirely 
without  pigment.  When  coloring-matter  is  present  it  often  con- 
sists of  chlorophyll,  or  some  allied  substance,  which  is  contained 
in  chromatophores,  e.g.  Euglena  (Fig.  22,  ^,  chr.).  Drinking 
water  is  often  colored  red  by  Euglena  sanguinea,  or  yellow  by 
Uroglena  (Fig.  26) ;  the  surface  of  the  sea  is  sometimes  colored 
orange  by  vast  numbers  of  Noctiluca  (Fig.  31),  or  red  by  a 
DiNOFLAGELLATE,  Peridiuium  (Fig.  30). 

The  simplest  kind  of  locomotor  organs  are  pseudopodia  like 
those  of  Ameba  (Fig.  9,  3).  The  pseudopodia  of  some  species 
have  a  firm  axial  rod  (Heliozoa,  Fig.  18),  and  those  of  others 
may  branch  and  fuse  with  one  another  (Foraminieera,  Fig.  20). 
Flagella  may  be  likened  to  very  thin  pseudopodia  that  have  be- 
come permanent.'  They  seem  to  be  composed  of  long  fibrils 
that  are  spirally  wound.     Cilia  are  smaller  and  more  numerous 


PHYLUM   PROTOZOA  67 

than  flagella;  often  they  are  fused  together  in  groups  forming 
large  cirri  {Stylonychia,  Fig.  43,  B),  or  side  by  side,  forming 
membranelles  as  in  the  gullet  of  Paramecium. 

An  external  covering  may  be  absent  from  the  body  of  Pro- 
tozoa (Ameba)  or  may  be  present  as  a  distinct  cuticle  (Para- 
mecium). Shells  may  also  occur;*  these  consist  of  material  se- 
creted by  the  animal,  e.g.  chitin  by  Arcella  (Fig.  16),  calcium 
carbonate  by  Foraminifera  (Fig.  21),  and  silica  by  Radio- 
LARIA  (Fig.  19),  or  are  made  up  of  foreign  particles  such  as 
grains  of  sand  {Difflugia,  Fig.  17). 

The  cytoplasm  of  Protozoa  is  probably  alveolar  in  structure. 
It  can  usually  be  separated  into  a  firm,  clear,  outer  layer,  the 
ectosarc,  and  a  more  fluid,  granular,  inner  mass,  the  endosarc. 
Within  the  cytoplasm  are  embedded  one  or  more  nuclei,  vacuoles 
of  several  kinds,  and  frequently  plastids. 

A  nucleus  is  always  present,  although  in  some  cases  its  essen- 
tial substance,  chromatin,  is  scattered  throughout  the  cells,  form- 
ing a  ''  distributed  nucleus."  Some  Protozoa  have  two  kinds 
of  nuclei,  a  macronucleus  {Paramecium^  Fig.  t^t^,  ma.),  which  is 
supposed  to  have  charge  of  the  metabolic  processes,  and  a  micro- 
nucleus  (Fig.  33,  mi.),  which  functions  only  in  reproduction. 
During  binary  division  the  chromatin  of  the  nucleus  may  form 
distinct  chromosomes,  but  in  many  cases  chromosomes  have  not 
been  observed. 

Vacuoles  are  of  several  kinds:  (i)  permanent  globules  of  liquid 
(Actinophrys,  Fig.  18),  (2)  contractile  vacuoles  (Ameba,  Fig.  9,  2), 
and  (3)  food  vacuoles  (Paramecium,  Fig.  33,/.?^.). 

Many  Protozoa  possess  plastids;  these  are  usually  bodies  of 
starchy  food  material,  or  colored  bodies  called  chromatophores, 
such  as  occur  in  Euglena.  Besides  these,  many  other  substances 
may  be  present,  such  as  food  material,  indigestible  matter,  oil 
drops,  grains  of  sand,  etc. 

Physiology.  —  Metabolism.  —  The  food  of  Protozoa  con- 
sists of  organic  matter  both  vegetable  and  animal.  Bacteria, 
diatoms,  and  other  Protozoa  form  a  large  part  of  the  bill  of  fare. 


68  COLLEGE  ZOOLOGY 

Such  species  as  Euglena  do  not  ingest  solid  food,  but  manufacture 
it  by  means  of  chlorophyll. 

Usually  some  structure  is  present  which  aids  in  the  ingestion 
of  food,  but  in  the  Rhizopoda,  like  Ameba,  there  is  no  mouth, 
and  food  is  engulfed  at  any  point  on  the  surface.  The  fiagella  of 
many  flagellates  and  the  cilia  of  ciliates  draw  or  drive  food  par- 
ticles toward  the  mouth  and  down  into  the  gullet  at  the  end  of 
which  a  food  vacuole  is  formed  (Paramecium,  Fig.  33,  /.  t^.)-  The 
SucTORiA  (Fig.  43,  D)  capture  their  prey  with  their  tentacles 
and  suck  the  contents  into  the  body.  Parasitic  Protozoa  take 
food  directly  through  the  surface  of  the  body. 

Digestion  takes  place  in  the  food  vacuoles,  which  are  really 
temporary  stomachs.  The  surrounding  protoplasm  secretes  fer- 
ments which  enter  the  vacuoles  and  dissolve  certain  food  sub- 
stances. Undigested  matter  is  cast  out  at  any  point  (Ameba), 
or  at  a  particular  spot  (Paramecium),  or  through  a  definite  anal 
opening  (Stentor).  Digested  food  passes  out  into  the  cytoplasm 
and  is  assimilated,  i.e.  is  transformed  into  protoplasm.  Figure 
6  indicates  that  oxygen  is  necessary  before  life  activities  can  be 
carried  on,  and  carbon  dioxide  is  given  off.  This  is  respiration. 
The  oxygen  is  taken  in  through  the  body- wall.  It  combines  with 
protoplasm,  i.e.  oxidation  takes  place.  Free  energy  is  a  result 
of  this  oxidation,  and  carbon  dioxide  and  other  waste  matter  in 
solution  are  by-products.  These  by-products  pass  out  through 
the  body-wall,  and  probably  by  way  of  the  contractile  vacuole. 
The  contractile  vacuole  may  therefore  be  called  a  primitive 
excretory  organ. 

From  the  above  discussion  it  may  be  concluded  that  the  Pro- 
tozoa carry  on  many  of  the  activities,  characteristic  of  the  higher 
organisms  without  the  aid  of  the  systems  of  organs  we  usually 
associate  with  these  functions. 

Behavior.  —  Locomotion.  —  Protozoa  move  from  place  to 
place  either  by  creeping  over  the  surface  of  objects  (Ameba,  Fig. 
9;  Stylonychia,  Fig.  43,  B),  or  by  free  swimming.  The  loco- 
motor organs  are  pseudopodia,  flagella,  and  cilia.     In  some  Pro- 


PHYLUM   PROTOZOA  69 

TOZOA  muscle  fibrils  (myonemes)  are  present  just  beneath  the 
cuticle  {Stentor,  Fig.  43,  A;  Vorticella,  Fig.  43,  C);  these  are 
capable  of  contraction  and  can  change  the  shape  of  the  animal. 
In  the  stalk  of  Vorticella  the  muscle  fibrils  are  agents  for  moving 
the  bell  from  place  to  place. 

Reactions  to  Stimuli.  —  Brief^accounts  have  been  given  of 
the  reactions  of  Ameba  (p.  35),  Euglena  (p.  43),  and  Paramecium 
(p.  56)  to  stimuli.  It  has  been  shown  that  these  minute  organ- 
isms are  capable  of  spontaneous  activities  and  respond  to  a  num- 
ber of  different  external  stimuli,  which  are  changes  in  their  en- 
vironment. These  responses  are  carried  on  without  the  help 
of  a  nervous  system.  The  study  of  the  behavior  of  the  lower 
organisms  has  become  quite  prominent  within  the  past  decade 
and  has  led  a  prominent  investigator  in  this  field  to  the  follow- 
ing conclusion.  "  All  together,  there  is  no  evidence  of  the  exist- 
ence of  differences  of  fundamental  character  between  the  be- 
havior of  the  Protozoa  and  that  of  the  lower  Metazoa.  The 
study  of  behavior  lends  no  support  to  the  view  that  the  life  ac- 
tivities are  of  an  essentially  different  character  in  the  Protozoa 
and  the  Metazoa.  The  behavior  of  the  Protozoa  appears  to  be 
no  more  and  no  less  machine-like  than  that  of  the  Metazoa; 
similar  principles  govern  both."  (Jennings,  Behavior  of  the 
Lower  Organisms,  p.  263.) 

Reproduction.  —  The  usual  method  of  reproduction  in  the 
Protozoa  is  that  of  binary  division.  This  occurs  in  most  of  the 
types  discussed  in  the  preceding  pages  {Ameba,  Euglena,  Para- 
mecium, etc.).  During  binary  division  the  body  of  the  Pro- 
TOZOON  divides  into  two  approximately  equal  parts,  the 
daughter-cells.  Binary  division  is  frequently  interrupted  by 
conjugation  as  in  Paramecium  (p.  59).  When  the  division  of 
the  Protozoon  is  unequal,  the  process  is  spoken  of  as  budding 
or  gemmation.  The  parasitic  Rhizopod,  Entameba  histolytica 
(p.  70),  reproduces  in  this  way.  A  third  method  of  reproduc- 
tion is  by  the  formation  of  spores  {Ameba,  p.  33;  MdnocystiSj 
P-  49,  Fig.  32). 


70  COLLEGE  ZOOLOGY 


6.  Pathogenic  Protozoa 


The  Protozoa  that  cause  diseases  are  said  to  be  pathogenic. 
One  of  the  best  known  of  these  is  the  malarial  fever  parasite, 
Plasmodium.  This  species  belongs,  with  many  other  important 
parasites,  to  the  class  Sporozoa,  but  all  protozoan  parasites  do 
not  belong  to  this  class.  There  are  many  injurious  parasites  in 
each  of  the  other  classes,  and  these  affect  both  man  and  other 
animals.  The  importance  of  pathogenic  Protozoa  has  but  re- 
cently been  recognized,  and,  although  a  vast  amount  of  work  has 
been  done  in  this  field,  still  comparatively  little  is  known  about 
them.  A  few  examples  of  those  affecting  man  are  described  in 
the  following  paragraphs. 

Rhizopoda.  —  Minute  ameba-like  organisms,  named  Enta- 
meba  histolytica,  are  the  cause  of  amebic  dysentery,  and  are  always 
found  in  the  aUmentary  canal  of  patients  suffering  from  this 
disease.  They  cause  ulcers  and  other  lesions  producing  enteritis. 
Other  ameboid  organisms,  which  are  probably  referable  to 
the  Rhizopoda,  accompany  hydrophobia  and  may  destroy  the 
nerve  cells  of  the  brain.  In  smallpox  similar  ameboid  organisms 
attack  and  destroy  the  epithelial  cells  of  the  skin.     Whether  or 

not  these  structures  are  the  direct 
cause  of  the  disease  mentioned  or 
are  merely  accessories  is  not  known, 
but  they  are  to  be  looked  upon  as 
dangerous  until  they  are  proved  to 
be  harmless. 
Fig.  44.  —  Trypanosoma  gam-       Mastigophora.  —  The    Trypano- 

biense    the  parasitic  Flagellate    ^^^^    ^g    ^^    ^^le    present    time    the 
which    causes    sleeping    sickness.  .  ^ 

(From  Calkins.)  most  widely  Studied  of  all  parasitic 

Mastigophora  that  affect  man. 
In  certain  parts  of  tropical  Africa  they  cause  the  disease  called 
trypanosomiasis,  commonly  known  as  sleeping  sickness.  Try- 
panosomes  are  also  parasitic  in  rats  and  other  animals.  The 
species  affecting  man  is  named  Trypanosoma  gambiense  (Fig.  44). 


PHYLUM   PROTOZOA 


71 


It  is  carried  from  one  person  to  another  by  a  certain  species  of 
tsetse- fly,  Glossina  palpalis  (Fig.  45).  The  parasite,  after  gain- 
ing access  to  the  blood  of  a  human  being,  multiplies  with  re- 
markable rapidity.  The  nervous  system  of  the  patient  is  af- 
fected either  directly  or  by  a  poison  secreted  by  the  parasites. 
The  disease  may  last  several  months  or  even  years.     Irregular 


Fig.  45- 


Glossina  palpalis,  the  tsetse  fly,  which  carries  the  germs 
of  sleeping  sickness.     (From  Calkins.) 


fever  soon  follows  infection,  and  later  general  debility  sets  in. 
The  victim  exhibits  an  increasing  tendency  to  sleep,  gradually 
wastes  away,  and  finally  dies. 

Sporozoa.  —  Of  the  Sporozoa  which  affect  man,  the  malarial 
fever  parasite  is  the  most  important  (pp..  50-52). 

Infusoria.  —  Two  species  of  parasitic  Ciliates  which  are  found 
in  the  intestine  of  human  beings  are  thought  by  some  investi- 
gators to  be  important  in  catarrhal  inflammation  of  the  intestine. 
They  are  Balantidium  coli  and  B.  minutum.     These  parasites 


72  COLLEGE  ZOOLOGY 

are  sometimes  found  within  the  mucous  lining  and  sometimes 
inside  of  the  muscular  layer  of  the  alimentary  canal,  and,  al- 
though they  have  not  been  proved  to  be  the  cause  of  any  disease, 
they  are  so  constantly  present  in  dysentery  patients  as  to  be 
looked  upon  as  dangerous. 


CHAPTE]^  III 
AN    INTRODUCTION   TO    THE    METAZOA 

The  Metazoa  (Gr.  meta,  beyond;  zodn,  animal)  are  animals 
consisting  of  many  cells.  These  cells  are  not  all  alike,  as  in  the 
colonial  Protozoa,  but  are  separated  into  groups  according  to 
their  structure  and  functions.  Although  every  Metazoon  be- 
gins its  existence  as  a  single  cell,  in  the  adult  stage  there  are  many 
cells,  and  one  kind  of  cell  cannot  exist  without  the  presence  of 
the  other  kinds  of  cells;  that  is,  the  cells  are  not  independent  as 
in  the  Protozoa,  but  are  dependent  upon  one  another.  This 
is  the  result  of  the  division  of  labor  among  the  cells. 

There  is  no  sharp  line  between  the  Metazoa  and  the  Protozoa. 
The  colonial  Protozoa  are  many-celled  animals,  and,  as  we  have 
seen  (p.  46),  Volvox  (Fig.  27)  consists  of  cells  which  are  made 
interdependent  by  protoplasmic  connections.  There  are  a  con- 
siderable number  of  animals  which  are  intermediate  between  the 
Protozoa  and  the  Metazoa,  but,  on  the  whole,  the  two  groups 
are  fairly  well  defined. 

I.   Germ-cells  and  Somatic  Cells 

There  are  two  chief  kinds  of  cells  in  all  the  Metazoa,  germ- 
cells  (Fig.  46,  A,  B)  and  somatic  cells  (Fig.  46,  C-G).  The  germ- 
cells,  like  those  in  Volvox  (Fig.  27,  ^  ,  $  ),  are  set  aside  for  reproduc- 
tive purposes  only  ;  the  somatic  cells  form  a  distinct  body,  which 
carries  on  all  the  functions  characteristic  of  animals  except  re- 
production. The  detailed  study  of  these  two  kinds  of  cells  in 
all  groups  of  the  Metazoa  has  led  to  the  idea  that  the  somatic 
cells  constitute  a  sort  of  vehicle  for  the  transportation  of  the  germ- 

73 


74 


COLLEGE  ZOOLOGY 


cells,  and  that  when  the  germ-cells  become  mature  they  separate 
from  the  body,  giving  rise  to  a  new  generation,  whereas  the 
somatic  cells  die. 

2.  Tissues 

The  somatic  or  body  cells  of  the  Metazoa  are  of  various  kinds, 
and  are  grouped  together  into  tissues.  A  tissue  is  an  association 
of  similar  cells  originating  from  a  particular  part  of  the  embryo 
and  with  special  functions  to  perform.  Some  of  the  simple 
Metazoa  possess  only  two  kinds  of  tissue;  others  are  made  up 
of  a  great  number.  The  many  different  kinds  of  tissues  may  be 
classified  according  to  their  structure  and  functions  into  four 
groups. 

(i)  Epithelial  tissue  (Fig.  46,  C)  consists  of  cells  which  cover 
all  the  surfaces  of  the  body  both  without  and  within.  In  the 
simpler  animals  this  is  the  only  kind  of  tissue  present.  In  the 
more  complex  animals  epithelial  cells  become  variously  modi- 
fied because  they  are  the  means  of  communication  between  the 
organism  and  its  environment;  nutritive  material  passes  through 
them  into  the  body,  and  excretory  products  pass  through  them 
on  their  way  out  of  the  body;  they  also  contain  the  end  organs 
of  the  sensory  apparatus,  and  protect  the  body  from  physical 
contact  with  the  outside  world.  In  man  the  cuticle  and  the 
lining  of  the  alimentary  canal  are  examples  of  epithelium. 

(2)  Supporting  and  Connective  Tissues  (Fig.  46,  D)  may  be 
encountered  in  almost  any  part  of  the  body.  Their  chief  func- 
tions are  (a)  to  bind  together  various  parts  of  the  body,  and 
(b)  to  form  rigid  structures  capable  of  resisting  shocks  and  pres- 
sures of  all  kinds.     These  tissues  consist  largely  of  non-living 

Substances,  fibers,  plates,  and  masses  produced  by  the  cells 
either  within  the  cell  wall  or  outside  of  it.  The  tendons  which 
unite  muscles  to  bones,  and  the  bones  and  cartilage,  illustrate 
the  two  kinds  of  tissue  in  this  group. 

(3)  Muscular  tissues  (Fig.  46,  E,  F)  are  the  agents  of  active 
movement.     In  certain  Protozoa  there  are  contractile  fibrils 


AN  INTRODUCTION  TO  THE   METAZOA 
A  C 


75 


.^'^  ' 


~mif  ¥#f  --/^  §i 


Fig.  46.  —  Various  kinds  of  cells.  A,  female  germ  cell,  ovum  of  a  cat.  B, 
male  germ  cell,  spermatozoon  of  a  snake.  Coluber.  C,  ciliated  epithelium  from 
the  digestive  tract  of  a  mollusk,  Cyclas.  D,  cartilage  of  a  squid.  E,  striated 
muscle  fiber  from  an  insect  larva,  Corydalis  cornutus.  F,  smooth  muscle  fibers 
from  the  bladder  of  a  calf.  G,  a  nerve  cell  from  the  cerebellum  of  man. 
(From  Dahlgren  and  Kepner.) 


76  COLLEGE  ZOOLOGY 

called  myonemes  in  the  membranous  coverings  (p.  69).  In  most 
of  the  higher  organisms  special  muscle  cells  are  differentiated  for 
performing  the  various  movements  of  the  body.  These  cells 
possess  muscle  fibrils  which  are  able  to  contract  with  great  force 
and  in  quick  succession.  The  fibrils  are  usually  of  two  kinds: 
(a)  cross-striated  (E),  and  (b)  smooth  non-striated  (F).  The 
latter  form  a  less  highly  developed  tissue  than  the  former  and 
are  found  in  the  simpler  inactive  animals,  and  in  those  internal 
organs  of  higher  organisms  not  subject  to  the  will  of  the 
animal. 

(4)  Nervous  tissue  (Fig.  46,  G)  is  composed  of  cells  which  are 
so  acted  upon  by  external  physical  and  chemical  agents  that  they 
are  able  to  perceive  a  stimulus,  to  conduct  it  to  some  other  cell 
or  cells  of  the  body,  and  to  stimulate  still  other  cells  to  activity. 
All  protoplasm  is  irritable;  animals  without  nervous  systems, 
e.g.  Ameba,  are  capable  of  reacting  to  a  stimulus,  but  in  more 
complex  organisms  certain  cells  are  specialized  for  the  sole  pur- 
pose of  performing  the  functions  described  above  as  character- 
istic of  nervous  tissue. 

3.  Organs  and  Systems  of  Organs 

An  organ  is  an  association  of  tissues  which  act  together  in 
the  performance  of  certain  functions.  For  example,  the  legs  of 
human  beings  are  organs  of  locomotion ;  they  consist  of  a  variety 
of  tissues,  including  epithelial  (skin),  muscular  (muscles),  'ner- 
vous (nerves),  and  supporting  (bones)  tissues. 

The  organs  of  different  animals  which  occupy  the  same  relative 
position  and  have  a  similar  origin,  i.e.  are  morphologically  equiv- 
alent, are  said  to  be  homologous.  Homologous  organs  may  have 
similar  functions,  e.g.  the  legs  of  man  and  the  hind  legs  of  the 
horse,  or  they  may  have  different  functions,  e.g.  the  arms  of 
man  and  the  wings  of  a  bird.  When  the  organs  of  different  ani- 
mals perform  the  same  functions  they  are  said  to  be  analogous^ 
e.g.  the  wing  of  a  bird  and  the  wing  of  a  butterfly.  In  many 
cases  homologous  organs  are  also  analogous,  being  morphologi- 


AN   INTRODUCTION   TO   THE    METAZOA  77 

cally  equivalent  and  having  the  same  functions,  e.g.  the  legs 
of  man  and  the  legs  of  a  bird. 

Many  organs  are  usually  necessary  for  the  performance  of  a 
single  function;  for  example,  the  proper  digestion  of  food  in  a 
complex  animal  requires  a  large  number  of  organs  collectively 
known  as  the  alimentary  canal  'Und  its  appendages.  These 
organs  constitute  the  digestive  system.  Similarly,  other  sets  of 
organs  are  associated  for  carrying  on  other  functions.  The 
principal  systems  of  organs  and  their  chief  functions  are  as  fol- 
lows: — 

(i)  Digestive  system  —  Digestion  and  absorption  of  food. 

(2)  Circulatory  system  —  Transportation  of  food,  oxygen,  and 
waste  products. 

(3)  Respiratory  system  —  Taking  in  oxygen  and  giving  off 
carbon  dioxide. 

(4)  Excretory  system  —  Elimination  of  waste  products  of 
metabolism. 

(5)  Muscular  system  —  Motion  and  locomotion. 

(6)  Skeletal  system  —  Protection  and  support. 

(7)  Nervous  system  —  Sensation  and  correlation. 

(8)  Reproductive  system  —  Reproduction. 

It  has  been  shown  in  Chapter  II  that  the  Protozoa  carry  on 
the  processes  of  digestion,  respiration,  excretion,  etc.,  without 
the  presence  of  definite  organs.  Likewise  many  of  the  simpler 
Metazoa  do  not  have  special  organs  for  the  performance  of  cer- 
tain functions,  but  the  more  complex  animals  are  provided  with 
well-developed  systems  of  organs.  The  following  paragraphs  give 
a  general  account  of  the  systems  of  organs  and  their  functions  in 
complex  animals. 

(i)  The  digestive  system  has  for  its  functions  the  changing 
of  solid  food  into  liquids  and  the  absorption  of  these  liquids  into 
the  blood.  This  system  consists  usually  of  a  tube,  the  alimentary 
canal,  with  an  opening  at  either  end  of  the  body.  Connected 
with  this  tube  are  a  number  of  glands.  Solids  taken  in  as  food 
are  usually  broken  up  in  the  mouth,  where  they  are  mixed  with 


78  COLLEGE   ZOOLOGY 

juices  from  the  salivary  glands;  the  mixture  then  passes  through 
the  oesophagus  into  the  stomach,  where  chemical  digestion,  aided 
by  secretions  from  the  gastric  glands,  takes  place;  it  then  enters 
the  intestine,  which  absorbs  the  dissolved  material  through  its 
walls.  Undigested  solids  travel  onward  into  the  rectum  and  are 
cast  out  through  the  anus  as  faeces. 

(2)  The  circulatory  system  transports  the  absorbed  food  to 
all  parts  of  the  body.  It  also  carries  oxygen  to  the  tissues  and 
carbon  dioxide  and  other  waste  products  away  from  the  tissues. 
These  substances  are  transported  by  fluids  called  blood  and 
ljm^,j\\^hiQh  are  usually  confined  in  tubes,  the  blood-vessels,  and 
in  irregular  spaces  known  as  sinuses.  The  blood  consists  of  a 
plasma  and  corpuscles.  It  is  forced  to  the  various  parts  of  the 
body  by  the  contractions  of  muscular  organs  called  hearts. 

(3)  The  respiratory  system  takes  in  oxygen  (inspiration)  and 
gives  off  carbon  dioxide  (expiration).  In  many  animals,  like 
the  earthworm,  the  oxygen  and  carbon  dioxide  pass  through  the 
moist  surface  of  the  body,  but  in  higher  animals  there  is  a  special 
system  of  organs  for  this  purpose.  Aquatic  animals  usually 
possess  gills  which  take  oxygen  from  the  water.  Terrestrial 
animals  generally  take  air  into  cavities  in  the  body,  such  as  the 
lungs  of  vertebrates  and  the  trachece  of  insects. 

(4)  The  excretory  system  is  necessary  for  the  elimination  of 
the  waste  products  of  metaboHsm  w^hich  are  injurious  to  the 
body.  These  waste  products  result  from  the  oxidation  of  the 
protoplasm.  Various  names  are  applied  to  the  organs  of  excre- 
tion such  as  nephridia  (Fig.  153,  neph.)  and  kidneys  (Fig.  417). 

(5)  The  muscular  system  enables  animals  to  move  about  in 
search  of  food  and  to  escape  from  their  enemies.  Many  animals, 
like  the  oyster,  have  the  power  of  motion,  but  not  of  locomotion. 
The  muscles  would  be  of  slight  efficiency  were  it  not  for  the  hard 
skeletal  parts  to  which  they  are  attached  and  which  serve  as 
levers. 

(6)  The  skeletal  system  is  either  external  (exoskeleton)  or 
internal  {end 0 skeleton).     The  hard  shell  of  the  crayfish  is  an 


AN   INTRODUCTION  TO  THE   METAZOA  79 

example  of  an  exoskeleton ;  the  bones  of  man  form  an  endoskele- 
ton.  In  either  case  the  skeleton  not  only  supports  and  protects 
the  soft  parts  of  the  body  but  also  provides  places  for  the  attach- 
ment of  muscles. 

(7)  The  nervous  system  in  higher  Metazoa  consists  of  two 
parts,  (a)  central  and  (b)  peripheral-  The  brain  and  spinal  cord 
constitute  the  central  nervous  system.  The  organs  of  special 
sense,  such  as  sight,  smell,  taste,  hearing,  touch,  temperature, 
and  equilibrium,  and  the  nerves  connected  with  them,  and 
all  other  nerves  connecting  the  central  nervous  system  with 
various  parts  of  the  body,  constitute  the  peripheral  nervous 
system.  Aferent  (sensory)  nerve  fibers  conduct  impulses  from 
end  organs  of  sense,  like  the  eye,  to  the  brain  or  spinal  cord. 
Eferent  (motor)  nerve  fibers  conduct  impulses  from  the  brain 
and  nerve  cord  to  an  active  organ  like  a  muscle  or  gland. 

(8)  The  reproductive  system  consists  of  the  germ-cells,  and  j 
the  organs  necessary  for  furnishing  yolk  and  protective  enve- 
lopes, and  for  insuring  the  union  of  the  eggs  and  spermatozoa  \ 
The  essential  reproductive  organs  in  complex  animals  are  usually 
the  ovaries  J  which  contain  the  eggs,  and  the  testes,  in  which  the 
spermatozoa  ripen.  The  accessory  organs  are  generally  ducts 
leading  to  the  exterior,  glands  connected  with  these  ducts,  and 
copulatory  organs. 

4.  Reproduction 

(i)  Methods  of  Reproduction.  —  In  the  Protozoa  reproduc- 
tion is  usually  by  binary  fission,  budding,  or  sporulation  (see 
pp.  32  and  49);  these  processes  may  be  preceded  by  conjuga- 
tion, which  is  a  temporary  or  permanent  union  of  tw^o  cells  (see 
pp.  59-62).  In  the  Metazoa  reproduction  is  usually  sexual, 
although  asexual  processes  are  normal  in  some  species. 

Sexual  Reproduction.  —  Reproduction  is  said  to  be  sexual 
when  the  individual  develops  from  a  mature  egg  which  usually 
fuses  with  a  spermatozoon  (pp.  84-85).  In  many  cases  the  egg 
does  not  unite  with  a  spermatozoon  before  development;   when 


8o  COLLEGE  ZOOLOGY 

this  occurs,  the  term  parthenogenesis  is  applied  to  the  process. 
For  example,  certain  eggs  of  plant  lice  (Aphids)  and  water  fleas 
(Daphnia)  normally  develop  parthenogenetic^lly.  In  a  few  cases 
animals  which  have  not  reached  maturity  produce  eggs  which 
develop  without  being  fertilized;  this  sort  of  parthenogenesis 
is  called  pcedogenesis.  For  example,  the  larvae  of  a  gall-gnat, 
and  the  pupae  of  a  midge,  produce  eggs  which  develop  without 
fertilization. 

A  species  of  animal  in  which  each  individual  possesses  only 
one  kind  of  reproductive  organs,  either  male  or  female,  is 
dioecious.  A  species  with  both  male  and  female  reproductive 
organs  in  the  same  individual  is  monoecious,  or  hermaphroditic. 
Hydra  (Figs.  65-72)  and  the  earthworm  (Figs.  153-159)  are 
examples  of  monoecious  animals;  the  crayfish  (Figs.  200-208) 
is  a  dioecious  species. 

If  the  eggs  of  a  monoecious  animal  are  fertilized  by  the  same 
individual,  self-fertilization  occurs;  whereas,  if  the  egg  of  one 
individual  unites  with  the  spermatozoon  of  another,  cross- 
fertilization  results. 

Animals  which  lay  eggs,  like  a  bird  or  crayfish,  are  oviparous; 
those  which  bring  forth  young  from  eggs  developed  within  the 
body,  like  mammals  and  certain  snakes,  viviparous. 

Asexual  Reproduction.  —  This  term  is  applied  to  reproduc- 
tion by  means  of  budding  or  fission,  and  not  by  the  production 
of  eggs.  By  fission  is  meant  the  division  of  the  parent  into 
two  or  more  equivalent  parts,  the  daughters.  This  occurs 
frequently  in  Protozoa  (Ameba,  p.  32,  Paramecium,  p.  59, 
Euglena,  p.  44),  and  less  often  in  Metazoa.  The  fresh-water 
flatworm,  Planaria  (Figs.  97-102),  and  the  annelid,  Dero,  often 
divide  by  fission.  The  offspring  produced  by  budding  are  smaller 
than  their  parent.  Hydra  (Fig.  65)  affords  an  excellent  example  . 
of  an  organism  that  reproduces  in  this  way. 

Metagenesis.  —  Some  animals  reproduce  by  budding  and 
do  not  develop  eggs  nor  spermatozoa.  Certain  of  the  buds, 
however,  separate  from  the  parent  and  produce  reproductive 


AN  INTRODUCTION  TO  THE  METAZOA 


8l 


cells  which,  after  fertilization,  grow  into  budding  individuals. 
There  is  here  an  alternation  of  an  asexual  budding  generation 
with  a  sexual  generation.  Obelia,  as  will  be  explained  later 
(Fig.  73),  develops  metagenetically. 

(2)  The  Origin  of  the  Egg  and  Spermatozoon.  —  Spermato- 
genesis. —  The  origin  of  the  male  germ-cell  or  spermatozoon 
is  termed  spermatogenesis.  As  shown  in  Figure  47,  this  process 
may  be  divided  into  three  periods:    (a)  the  multiplication  of 


PRIMORDIAL 
GERM-CELL 


SPERMATOGONIA^-- 


MULTIPLICATIOM 
PERIOD 


MATURATION 
PERIOD 


Fig.  47. 


-  Diagram  illustrating  the  stages  of  spermatogenesis.     The  primordial 
germ-cell  is  represented  as  possessing  four  chromosomes. 


the  primordial  germ-cells  or  spermatogonia,  (b)  the  growth 
of  these  cells,  and  (c)  their  ripening  or  maturation.  These 
stages  occur  in  all  Metazoa  from  the  lowest  to  man. 

No  one  knows  how  many  cells  are  produced  during  the  period 
of  multiplication.  The  last  generation  of  spermatogonia  gives 
rise  by  division  to  the  primary  spermatocytes.  The  latter  increase 
greatly  in  size  during  the  long  growth  period,  and  in  each  of 
them  the  chromosomes  unite  or  conjugate  to  form  double  or 
bivalent  chromosomes.  Each  primary  spermatocyte  gives  rise 
by  division  to  two  secondary  spermatocytes.  The  secondary 
spermatocytes  immediately  divide,  each  forming  two  spermatids. 


82 


COLLEGE  ZOOLOGY 


In  one  of  these  divisions  the  chromosomes,  which  united  to  form 
the  bivalent  chromosomes,  separate,  one  single  or  univalent 
chromosome  going  to  each  daughter  cell.  This  is  the  only  known 
case  in  cell  division  where  entire  chromosomes  are  separated 
from  one  another,  except  the  corresponding  stage  in  oogenesis. 
It  is  know^n  as  a  reduction  division  because  it  results  in  a  reduc- 
tion in  the  number  of  chromosomes  to  one  half  in  the  daughter 
cells.  After  these  two  maturation  divisions,  as  they  are  called, 
the  spermatids  are  metamorphosed  into  spermatozoa  (Fig.  46,  ^). 


PRIWORDIAL 
GERM-CELL 


MULTIPLICATION 
PERIOD 


PRIMARY  /  \  >    ^^""^^^ 

OOCVTE  (     1%^  ^     ''"•°° 

SECONDARY 
OOCYTES 
(OVARIAN  EGG  \     "    "     }  K^  \     MATURATION 

AND  POLAR  BODY)  X.  /  /\  >  PERIOD 

MATURE  EGG  /^        >.     \_^  j/ 

AND  (    ,    o      1     (^      rt 

POLAR  BODIES  V  /    ^--^     ^-^ 

Fig.  48.  — Diagram  illustrating  the  stages  of  oogenesis.     The  primordial 
germ-cell  is  represented  as  possessing  four  chromosomes. 

The  Spermatozoa  of  various  animals  are  usually  easily  distin- 
guished one  from  another,  but  are  mostly  constructed  on  the 
.same  plan.  They  resemble  an  elongated  tadpole  (Fig.  46,  B), 
having  a  head  filled  almost  entirely  with  nuclear  material  and 
a  long  flagellum-like  tail  which  is  the  organ  of  locomotion;  a 
middle  piece  joins  these  two.  The  spermatozoa  are  the  active  j 
germ-cells.  It  is  their  function  to  seek  out  and  fertilize  tl;^ 
larger  stationary  egg  cells.  Frequently  they  are  only  y^oiro^o" 
the  size  of  the  egg,  and  in  the  sea-urchin,  Toxopneustes,  their 
bulk  is  about  -g-oijoTro  the  volume  of  the  ovum. 


AN   INTRODUCTION  TO  THE  MET,\ZOA 


83 


Oogenesis.  —  The  origin  of  the  female  germ  cell  or  egg  is 
called  oogenesis  (Fig.  48).  Stages  are  passed  through  by  the 
germ  cells  corresponding  almost  exactly  to  those  described  under 
spermatogenesis  (Fig.  47).  Before  the  growth  period  the  germ- 
cells  which  will  produce  eggs  are  known  as  oogonia  (Fig.  46,  A ; 


p.b.i-- 


p.5.i.^.t 


d 


h 


Fig.  49.  —  Diarrrams  illustrating  the  maturation,  fertilization,  and  cleavage 
of  an  egg.  The  primordial  germ-cell  is  represented  as  possessing  four  chro- 
mosomes. 


84  COLLEGE  ZOOLOGY 

Fig.  48;  Fig.  49,  a).  At  the  completion  of  the  growth  period 
they  are  termed  primary  oocytes  (Fig.  49,  b).  The  primary 
oocytes  contain  only  one  half  the  number  of  chromosomes  char- 
acteristic of  the  somatic  cells  and  oogonia.  As  in  the  primary 
spermatocytes,  these  chromosomes  are  bivalent,  resulting  from 
the  union  two  by  two  of  the  univalent  chromosomes  of  the 
oogonia.  The  primary  oocyte  divides  in  the  following  manner. 
Its  nucleus,  called  the  germinal  vesicle  (Fig.  49,  a),  moves  to  the 
periphery  (b),  where  a  mitotic  figure  is  formed  perpendicular 
to  the  surface  of  the  egg  (c).  A  small  bud-like  protrusion  is  now 
formed  into  which  pass  one  univalent  chromosome  from  each  of 
the  bivalent  chromosomes  present  in  the  primary  oocyte  (d). 
The  bud  is  then  pinched  off.  Two  secondary  oocytes  are  pro- 
duced by  this  division,  each  containing  an  equal  amount  of 
chromatin,  but  one  with  a  great  deal  more  cytoplasm  and  yolk 
than  the  other  (e).  The  small  one  is  known  as  the  first  polar 
body  (e,  p.b.  i)  and  is  not  functional;  the  larger  is  the  egg. 
Each  secondary  oocyte  now  prepares  for  division  (e).  The  first 
polar  body  in  some  cases  does  not  divide;  when  it  does,  the  divi- 
sion is  equal  (g,  p.b.  i).  The  egg  throws  off  a  second  polar  body 
(g,  p.b.  2),  which  contains  one  half  of  each  chromosome.  This 
second  polar  body  disintegrates,  as  does  the  first. 

(3)  Fertilization.  —  The  mature  ovum  now  becomes  the  center 
of  the  interesting  process  of  fertilization.  The  spermatozoon 
sometimes  enters  the  egg  before  the  polar  bodies  are  formed,  and 
sometimes  afterward.  In  the  illustration  (Fig.  49,  e)  the  sperm 
is  shown  entering  the  egg  at  the  end  of  the  first  oocyte  division. 
The  sperm  brings  into  the  egg  a  nucleus,  a  centrosome,  and  a 
very  small  amount  of  cytoplasm.  The  sperm  nucleus  soon 
grows  larger  by  the  absorption  of  material  from  the  cytoplasm 
of  the  egg,  and  the  centrosome  begins  its  activity.  A  mitotic 
figure  soon  grows  up  (g)  and  moves  toward  the  center  of  the  egg. 
The  egg  nucleus  also  moves  in  this  direction  (h),  and  finally  both 
the  male  and  female  nuclei  are  brought  together  in  the  midst 
of  the  spindle  produced  about  the  sperm  nucleus   (i).     This 


AN  INTRODUCTION  TO  THE   METAZOA  85 

completes  the  process  usually  known  as  fertilization.     In  this 
process  the  chief  aim  so  far  seems  to  be  the  union  of  two  nuclei^ 
one  of  maternal  origin,  the  other  of  paternal  origin.     We  shall  see    j 
later  that  fertilization  is  really  not  consummated  until  the  ani- 
mal which  develops  from  the  egg  has  become  sexually  mature. 

Chromosome  Reduction.  —  It  is  now  possible  to  point  out 
the  result  of  the  reduction  in  the  member  of  chromosomes  which 
takes  place  during  maturation.  It  has  already  been  stated 
(p.  16)  that  every  species  of  animal  has  a  definite,  even  number 

of  chromosomes  in  its  somatic  cells.     This  number  remains  con- j 

stant,  generation  after  generation.  Now  if  the  mature  egg  con- 
tained this  somatic  number  of  chromosomes  and  the  sperm 
brought  into  it  a  like  number,  the  animal  which  developed 
from  the  fertilized  egg  would  possess  in  its  somatic  cells  twice 
as  many  as  its  parents.  The  number  is  kept  constant  by  re^^ 
duction  _  during  the  maturation  divisions,  so  that  both  egg  and 
sperm  contain  only  one  half  the  number  in  the  somatic  cells. 
The  union  of  egg  and  sperm  again  establishes  the  normal  num- 
ber of  chromosomes  possessed  by  the  parents. 

Union  of  Chromosomes  in  Fertilization.  —  If  we  return 
for  a  moment  to  the  subject  of  maturation,  the  final  process  in 
fertilization  may  be  understood.     It  appears  that  chance  has 
very  little  to  do  with  the  union  of  chromosomes  in  pairs  during 
the  early  history  of  the  germ-cells  (pp.  81-84,  Figs.  47,  48,  49) ; 
but  that  one  chromosome  of  each  pair  came  originally  from  the 
egg  and  is  therefore  maternal,  while  the  other  was  derived  from 
the  sperm,  and  is  paternal.    Since  the  chromosomes  are  recognized"^ 
as  the  bearers  of  hereditary  qualities,  it  follows  that  the  blending 
of  the  characteristics  of  the  mother  and  the  father  in  the  germ- 
cells  does  not  occur  when  the  sperm  enters  the  egg,  but  when    [ 
the  individual  developing  from  the  zygote  becomes  sexually    I 
mature.  — ^, 

(4)    Embryology.  —  Cleavage.  —  The   di\dsion   of   the   fer-     | 
tilized  egg  is  known  as  cleavage.     The  chromatin  of  the  united 
germ  nuclei  condenses  into  chromosomes,  which  are  so  arranged 


86 


COLLEGE   ZOOLOGY 


on  the  first  cleavage  spindle  (Fig.  49,  j)  that  each  daughter 
nucleus  receives  half  of  each.  This  means  that  each  daughter 
cell  will  contain  half  of  each  chromosome  of  paternal  origin  and 
half  of  each  chromosome  of  maternal  origin.  Further  mitotic 
(divisions  insure  a  like  distribution  to  every  cell  in  the  body. 

After  nuclear  division 
comes  the  division  of 
the  entire  cells  into  two 
{k  and  I). 

Typically  the  ferti- 
lized egg  divides  into 
two  cells,  these  two 
into  four,  these  four 
into  eight,  etc.,  each 
cleavage  plane  being 
perpendicular  to  the 
last  preceding  plane 
(Fig.  51).  This  is 
known  as  total  cleamge^ 
and  is  characteristic  of 
holohlastic  eggs.  Other 
eggs  are  said  to  be 
'ni.pjnhlg^lQ  and  exhibit 
f^^rtjal  cleamse :  that  is, 
only  a  sj^U  part  of  the 
egg  enters  into  cell 
division,  the  remainder 
serving  as  nutritive 
material  for  the  cleav- 
age cells.  In  all  we 
"can  recognize  four  distinct  types  of  cleavage:  (i)  equal  cleavage, 
where  the  egg  divides  into ^ two  equal  halves  (Fig.  50,  A); 
(2)  unequal  cleavage,  where  the  first  division  of  the  egg  results 
in  one  large  and  one  small  cell  (Fig.  50,  B) ;  (3)  discoidal  cleavage, 
where  the  entire  egg  does  not  di\dde,  but  small  cells  are  cut  off 


•,  Fig.  so.  —  Figures  illustrating  four  different 
kinds  of  cleavage.  A,  equal  cleavage  of  the  sea- 
urchin  egg.  B,  unequal  cleavage  of  the  egg  of 
a  marine  worm.  C,  discoidal  cleavage  of  the 
egg  of  a  squid.  D,  superficial  cleavage  of  an 
insect's  egg.  (A-B,  from  Wilson ;  C,  from 
Wilson,  after  Watase;  D,  from  Korschelt  and 
Heider.) 


AN  INTRODUCTION  TO  THE  METAZOA  87 

at  the  surface  and  form  a  disc-shaped  region  (Fig.  50,  C) ;  and 
(4)  superficial  cleavage,  where  the  nucleus  of  the  egg  divides 
rapidly;  the  daughter  nuclei  migrate  to  the  periphery  and  form 
a  single  layer  of  cells  at  the  surface  (Fig.  50,  D). 

That  part  of  ontogeny  which  concerns  the  development  of  an 
animal  from  the  egg  to  maturity  is  known  as  ^brynEcny.  Cer- 
tain stages  in  this  development  have  been  recognized  as  common 
to  all  higher  animals,  and  have  been  given  names.  The  stages 
occur  in  a  certain  regular  order,  as  follows:  (i)  cleavage,  (2) 
the  morula,  (3)  the  blastula,  (4)  the  gastrula,  (5^  the  formation  of 
germ-layers,  and  (6)  organogeny. 

Cleavage  in  a  holoblastic  egg  (Fig.  51,  ^)  results  in  the  pro- 
duction of  two  (B),  four  (C,  D),  eight  (£),  sixteen  (F),  etc. 
cells  approximately  equal  to  one  another  and  growing  smaller  as 
their  number  increases.  Each  of  these  cells  is  known  as  a 
blastqimx£.  The  blastomeres  do  not  separate  as  do  the  daughter 
cells  produced  by  the  binary  division  of  Paramecium  (Fig.  40, 
o-q),  but  remain  attached  to  one  another.  The  resemblance^ 
of  the  group  of  blastomeres  to  a  mulberry  suggested  the  term 
,^^/fl,  which  is  often  used  in  describing  the  egg  during  the 
early  cleavage  stages.  .^ 

Blastula.  —  As  cleavage  advances,  a  cavity  becomes  notice- 
able in  the  center  of  the  egg  (Fig.  51,  fl")  enlarging  as  develop- 
ment proceeds  until  the  whole  resembles  a  hollow  rubber 
ball,  the  rubber  being  represented  by  a  single  layer  of  celly. 
At  this  stage  the  egg  is  called  a  blastula,  the  cavity  the  cleavage 
or  segmentation  cavity,  and  the  cellular  layer  the  blastoderm. 
The  blastula  resembles  somewhat  a  single  colony  of  Volvox 
(Fig.  27). 

Gastrula. — The  cells  on  one  side  of  the  blastula  are  seen 
to  be  thicker  than  elsewhere  (Fig.  51,  K)  and  begin  to  invagi- 
nate  (Fig.  51,  L).  This  process  results  in  a  cup-shaped  struc- 
ture with  a  wall  of  two  layers,  an  outer  layer  of  small  cells  and 
an  inner  layer  of  larger  cells.  The  embryo  may  now  be  called 
a  gastrula  (M),  and  the  process  by  which  it  developed  from  the 


88 


COLLEGE  ZOOLOGY 


Fig.  51.  —  Figures  illustrating  the  cleavage  of  the  holoblastic  egg  of  Am- 
phioxus,  and  the  formation  of  germ  layers.  A-K,  cleavage  and  formation  of 
the  blastula.  L-M,  gastrulation.  N,  production  of  the  mesoderm  and 
ccelomic  cavities.  O,  coelom  further  developed,  ak,  ectoderm;  dh,  primitive 
alimentary  canal;  ik,  entoderm;  mki,  somatic  layer  of  mesoderm;  mk^, 
splanchnic  layer  of  mesoderm.     (From  Korschelt  and  Heider,  after  Hatschek.) 


AN  INTRODUCTION  TO  THE  METAZOA  89 

blastula  is  termed  gastruloMon.  The  cleavage  cavity  is  almost 
obliterated  during  the  invagination,  while  a  new  cavity,  the 
-primitive  digestive  tract  or  archenkron^js .  established^ 

Germ-layers.  —  The  cells  of  one  layer  of  the  gastrula  resemble  ^ 
one  another,  but  differ  in  appearance  from  the  cells  of  the  other  I 
layer.  Each  layer  gives  rise  to  certain  definite  parts  of  the 
body,  and  is  therefore  termed  a  germ-layer;  the  outer  is  the 
ectoderm  (Fig.  51,  N,  ak),  the  inner,  the  entoderm  (N,  ik).  Ani- 
mals with  only  these  two  layers  are  said  to  be  diplohlastic ;  but 
the  majority  of  the  higher  animals  have  a  third  layer  which 
usually  appears  between  the  first  two  after  the  gastrula  has  been 
formed.  This  is  the  middle  layer  or  mesoderm.  It  originates 
either  from  the  proliferation  of  a  few  special  cells  which  may  be 
recognized  in  the  early  cleavage  stages,  or  from  cells  budded  off 
from  the  inner  surface  of  both  the  ectoderm  and  entoderm, 
or  from  pouches  arising  from  the  walls  of  the  entoderm  (Fig. 
51,  iV).  Animals  with  three  germ-layers  are  said  to  be  triplo- 
blastic. 

The  tissues  developing  from  the  germ-layers  are,  in  part,  as 
follows.  From  the  ectoderm  arise  the  epidermis,  epithelium  of 
vanous  organs,  and  the  nervous  system;  from  the  mesoderm 
come  the  muscles,  connective  and  supporting  tissues,  and  blood 
and  blood-vessels;  the  entoderm  becomes  the  epithelium  of  the 
digestive  tract,  pharynx,  and  respiratory  tract. 

CcELOM.  —  The  ccelom  is  a  ca\ity  in  the  mesoderm  lined  by 
an  epithelium;  into  it  the  excretory  organs  open,  and  from  its 
walls  the  reproductive  cells  originate.  There  is  no  ccelom  in 
the  lower  Metazoa,  but  one  is  present  in  all  the  more  complex 
animals.  As  shown  in  Figure  51,  A",  0,  it  arises  in  a  typical 
animal  as  cavities  of  the  mesodermal  pouches  which  form  from 
the  primitive  alimentary  canal  (iY,  dh).  The  outer  mesodermal 
lining  of  the  ccelomic  cavities  is  called  the  somatic  epithelium  (O. 
mki),  and  the  inner  the  splanchnic  epithelium  (O,  mk<^.  The 
importance  of  the  ccelom  both  morphologically  and  physiologi- 
cally will  be  discussed  later. 


go  COLLEGE  ZOOLOGY 

5.   The  Forms  of  Animals 

Although  most  animals  pass  through  similar  stages  in  their 
development  from  the  egg,  the  adult  organisms  differ  widely 
in  the  form  of  their  bodies.  This  is  a  result  of  two  factors:  (i) 
the  initial  structure  of  the  germ,  and  (2)  the  influence  of  the 
environment.  Differences  in  the  form  of  animals  are  due 
principally  to  symmetry,  metamerism,  and  the  character  of  the 
appendages. 

Symmetry.  —  Animals  are  either  symmetrical  or  asymmetrical. 
The  symmetrical  animals  may  be  divided  into  two  types:  (i) 
radially  symmetrical,  and  (2)  bilaterally  symmetrical. 

A  radially  symmetrical  animal  possesses  a  number  of  similar 
\^^arts,  called  antimeres,  which  radiate  out  from  a  central  axis. 
The  adult  starfish  (Fig.  131)  is  a  good  example;  its  arms  are 
similar  and  radiate  out  from  the  central  disc.  Some  simple 
sponges  (Fig.  55),  the  majority  of  the  Ccelenterata  (Fig.  79), 
and  most  adult  Echinodermata  are  radially  symmetrical. 
Radial  symmetry  is  best  suited  to  sessile  animals,  since  the 
similarity  of  the  antimeres  enables  them  to  obtain  food  or  repel 
enemies  from  all  sides. 

The  bodies  of  bilaterally  symmetrical  animals  are  so  constructed 
that  the  chief  organs  are  arranged  in  pairs  on  either  side  of  an 
axis  passing  from  the  head  or  anterior  end  to  the  tail  or  posterior 
end.  There  is  only  one  plane  through  which  their  bodies  can 
be  divided  into  two  similar  parts.  An  upper  or  dorsal  surface 
and  a  lower  or  ventral  surface  are  recognizable,  as  well  as  right 
and  left  sides.  Bilateral  symmetry  is  characteristic  of  the  most 
successful  animals  living  at  the  present  time,  including  all  of 
the  vertebrates  and  most  of  the  invertebrates. 

Metamerism.  —  Metameric  animals  have  bodies  composed 
of  more  or  less  similar  parts  or  organs  arranged  in  a  linear  series 
along  the  main  axis.  Each  part  is  called  a  metamere,  somite, 
or  segment.  In  many  animals  metamerism  is  not  shown  by  the 
external  structures,  but  is  exhibited  by  the  internal  organs ;   this 


AN   INTRODUCTION  TO  THE  METAZOA 


91 


is  true  of  the  vertebrates,  which  have  the  vertebrae  of  the  back- 
bone, the  ribs,  and  nerves  metamerically  arranged.  The  earth- 
worm (Fig.  154)  is  a  good  illustration  of  both  external  and  in- 
ternal metamerism;  the  body  consists  of  a  great  number  of 
similar  segments,  and  the  ganglia  of  the  nerve  cord,  the  cham- 
bers of  the  body  cavity  and  the  excij^etory  organs  are  segmentally 
arranged.  _^ . 

The  earthworm  may  serve  also  as  an  example  of  an  animal 
with  homonomous  segmentation ^  since  the  metameres  are  similar. 
The  crayfish  (Fig.  202),  on  the  other  hand,  is  a  heteronomous 
animal,  since  division  of  labor  has  resulted  in  the  dissimilarity 
of  the  metameres  of  different  regions  of  the  body.  The  verte- 
brates, including  man,  are  all  heteronomous. 

Appendages.  —  The  external  appendages  of  animals  are  out- 
growths of  the  body,  which  are  used  for  locomotion,  obtaining 
food,  protection,  respiration,  and  many  other  purposes.  They 
are  greatly  modified  for  their  various  functions,  and  these 
modifications  furnish  excellent  material  for  the  study  of  homolo- 
gous and  analogous  organs.  For  example,  the  fins  of  fishes,Jhje 
wings  of  birds,  and  the  arms  of  man  serve  to  distinguish  their 
bearers  from  one  another;  nevertheless,  these  structures  are 
homologous,  since  they  are  morphologically  equivalent. 


CHAPTER  IV 
PHYLUM   PORIFERA 

The  members  of  the  Phylum  Porifera  (Lat.  porus,  a  pore; 
ferre,  to  bear)  are  commonly  called  sponges.  The  ordinary  bath 
sponge  of  commerce  is  the  skeleton  of  one  of  these  animals. 
Most  sponges  live  only  in  salt  water.  Formerly  they  were 
considered  plants  because  of  their  irregular  and  plantlike  habits 
of  growth.  When  their  animal  nature  was  finally  established 
(about  1857),  the  problem  of  their  position  in  the  animal  series 
arose.  By  many  authorities  they  were  considered  colonial 
Protozoa  allied  with  the  Choanoflagellata  (p.  47),  but  they 
are  now  generally  classed  with  the  many-celled  animals,  and 
placed  in  a  separate  group,  the  Parazoa,  as  explained  on 
page  24. 

Sponges  may  be  grouped  into  three  classes  according  to  the 
composition  and  shape  of  their  skeletal  elements  (spicules) :  — 

Class  I.  Calcarea  (Lat.  calcarius,  lime)  with  spicules  of 
carbonate  of  lime  (Fig.  53); 

Class  II.  Hexactinellida  (Gr.  hex,  six;  aktin,  a  ray) 
with  triaxon  spicules  of  silicon  (Fig.  60,  e);   and 

Class  III.  Demospongi^  (Gr.  demos,  people;  spongos, 
sponge)  usually  with  spicules  of  silicon,  not  triaxon,  or  with 
spongin  (Fig.  61),  or  with  both  spicules  and  spongin. 

I.   Structure  of  a  Simple  Sponge  —  Leucosolenia 

Leucosolenia  (Fig.  52)  is  a  sponge  which  will  serve  to  illustrate 
the  structure  of  the  most  simple  members  of  the  phylum. 
It  is  found  growing  on  the  rocks  near  the  sea-shore  just  below 

92 


PHYLUM  PORIFERA 


93 


dsc 


ai^ 


Fig.  52.  —  A  small  colony  of  Leucoso- 
lenia,  a  simple  sponge,  osc,  osculum  ; 
div;  side  branches.  (From  Lankester's 
Treatise  on  Zoology.) 


low-tide  mark,  and  consists  of  a  number  of  horizontal  tubes  from 
which  branches  extend  up  into  the  water.  These  branches  have 
an  opening,  the  osculum  (osc), 
at  the  distal  end,  and  buds 
and  branches  {div)  projecting 
from  their  sides.  The  buds 
and  branches  are  hollow,  pos- 
sessing a  single  gastral  cavity 
(Fig.  59,  A,  GC)  which  com- 
municates with  the  horizontal 
tubes.  The  entire  mass  is  a 
colony  of  animals,  and  the 
tissues  connected  with  a 
single  osculum  may  be  con- 
sidered an  individual  sponge. 
If  a  branch  is  examined 
under  a  microscope,  it  will  be  found  to  contain  a  large  number 
of  three-pronged  (triradiate)  spicules,  which  are  embedded  in 

the  soft  tissue  of 
the  body- wall  (Fig. 
53)  ;  these  serve  to 
strengthen  the  body 
and  hold  it  upright. 
The  appUcation  of 
acid  results  in  the 
dissolution  of  these 
spicules  and  the 
production  of  an 
effervescence,  thus 
proving  them  to  be 
composed  of  cal- 
cium carbonate. 
The  body-wall  is 
so  flimsy  that  it  is 
difficult    to    study 


Fig.  53. — Z,eMC05o/ewia,  a  simple  sponge.  View  of 
a  branch  showing  the  sieve-like  membrane  (i)  which 
stretches  across  the  osculum.  The  lower  part  shows 
spicules  only.  (From  Shipley  and  MacBride,  after 
Minchin.) 


94  COLLEGE  ZOOLOGY 

even  under  the  best  conditions.  It  is  made  up  of  two  layers  of 
cells :  an  outer  layer,  the  dermal  epithelium,  and  an  inner  layer, 
the  gastral  epithelium.  These  layers,  as  will  be  shown  later 
(p.  104),  are  not  comparable  to  the  ectoderm  and  entoderm  of 
the  CcELENTERATA  and  other  Metazoa.  Between  these  two 
layers  is  a  jelly-like  substance  similar  to  the 
mesoglea  of  Hydra  (p.  109)  in  which  are  many 
ameba-like  wandering  cells. 

The  gastral  epithelium  is  peculiar,  since  it 
consists  of  a  single  layer  of  collar  cells,  the 
choanocytes  (Fig.  54),  which  resemble  the 
similar  cells  of  the  choano  flagellate  Protozoa 
(Fig.  29).  The  flagella  of  these  collar  cells 
Fig.  54.  —  A  beat  constantly,  creating  a  current  of  water, 
single    collar  cell  jf  ^  ij^tle  Coloring  matter  is  placed  in  the  water, 

of      Leucosolenia.    .        .  or-  7 

n,  nucleus.  (From  it  will  be  drawn  into  the  animal  through  minute 
Natur^afffistory!  ^^'^'^^^^  P^'^'^  the  ostia  (Fig.  59,  A,  p),  in  the 
after  Bidder.)  '  body- wall  and  will  pass  out  through  the  openings 
in  a  sieve-like  membrane  stretched  across  the 
osculum  (Fig.  53,  /).  The  osculum  is  therefore  the  exhalant 
opening,  and  not  the  mouth,  as  a  casual  examination  might 
lead  one  to  believe.  The  course  of  the  current  of  water  in 
such  a  sponge  is  shown  by  arrows  in  Figure  59,  A.  The 
presence  of  the  incurrent  pores  suggested  the  name  Porifera 
for  members  of  this  phylum. 


2.  Anatomy  and  Physiology  of  Grantia 

Grantia  (Fig.  55)  is  also  known  as  a  simple  sponge,  though 
it  is  more  complex  than  Leucosolenia.  It  lives  in  the  salt  water 
along  the  sea-coast  and  is  permanently  attached  to  the  rocks  and 
piles  just  below  the  low-tide  mark.  It  is  shaped  like  a  vase 
that  bulges  in  the  middle,  and  is  about  three-fourths  of  an  inch 
long.  Frequently  huds  occur  near  the  base,  and  a  small  colony 
is  formed. 


PHYLUM   PORIFERA 


95 


Structure.  —  A  longitudinal  section  of  Grantia  (Fig.  56) 
shows  that  the  body  possesses  a  single  cavity  as  in  Leucosolenia, 
but  the  body  wall  is  much  thicker.  This  condition  has  been 
brought  about  by  the  folding  of  the  wall  of  a  larval  stage  which 
resembles  Leucosolenia,  resulting  in  the  production  of  a  series 
of  parallel  canals.  Part  of  these  are  incurrent  canals  and  open 
to  the  outside  (Fig.  59,  B,  inc)\  the  rest  open  into  the  gastral 
cavity  (C.C),  are  Hned  with  choanocytes  (Fig.  54),  and  are 
called  flagellated  chambers  or  radial  canals 
(Fig.  59,  Byfl.c).  The  area  covered  by 
collar  cells  is  enormously  increased  in 
this  way  (compare  the  black  layers  in 
Fig.  59,  A  and  B).  Water  enters  the 
body  of  Grantia  as  shown  by  arrows  in 
Figure  59,  B,  by  way  of  the  incurrent 
canals  (inc.)  ;  from  these  it  passes 
through  pores,  called  prosopyles  {pr.p), 
into  the  radial  canals  (/.c),  then  through 
the  apopyles  (ap.p)  into  the  gastral 
cavity  (G.C.),  and  finally  out  of  the 
osculum  (osc). 

As  in  Leucosolenia,  Grantia  possesses 
an  outer  dermal  layer  of  cells,  an  inner 
gastral  epithelium  made  up  of  collar  cells 

which  line  the  radial  canals,  and  a  middle  jelly-like  substance 
in  which  are  a  number  of  wandering  ameboid  cells.  The  last- 
named  cells  are  considered  by  some  authorities  equivalent  to 
the  mesoderm  of  higher  animals,  but  this  is  probably  not  the 
case. 

The  skeleton  of  Grantia  consists  of  calcareous  spicules,  of 
which  there  are  four  varieties:  (i)  long,  straight  monaxon  rods 
guarding  the  osculum,  (2)  short,  straight  monaxon  rods  surround- 
ing the  incurrent  pores,  (3)  triradiate  spicules  always  found  em- 
bedded in  the  body- wall,  and  (4)  T-shaped  spicules  lining  the 
gastral  cavity;  four-  and  five-rayed  spicules  may  also  be  found. 


-  A  simple 
(After  Minchin.) 


96 


COLLEGE  ZOOLOGY 


Spicules  are  built  up  within  cells  called  sderoblasts,  which  form 
part  of  the  inner  stratum  of  the  dermal  layer. 

Physiology.  —  Grantia  lives  upon  the  minute  organisms  and 
small  particles  of  organic  matter  that  are  drawn  into  the  incur- 
rent  canals  by  the  current  of  water  produced  by  the  beating  of 

the  collar-cell  flagella. 
The  majority  of  the 
food  particles  are  en- 
gulfed by  the  collar 
cells.  Digestion,  as  in 
the  Protozoa,  is  intra- 
cellular, food  vacuoles 
being  formed.  The  dis- 
tribution of  the  nutri- 
ment is  accomplished 
by  the  passage  of 
digested  food  from  cell 
to  cell,  aided  by  the 
ameboid  wandering  cells 
of  the  middle  layer. 

Excretory    matter    is' 
discharged  through  the, 
general    body    surface,  I 
assisted    probably    by  \ 
the  ameboid  wandering  • 
cells,   and   possibly   by 
the    collar    cells,    also. 
Respiration    likewise 
takes  place,  in  the  ab- 
sence of  special  organs,  through  the  cells  of  the  body-wall. 

Reproduction.  —  Reproduction  in  Grantia  takes  place  by 
both  sexual  and  asexual  methods.  In  the  latter  case,  a  hud 
arises  near  the  point  of  attachment,  finally  becomes  free,  and 
takes  up  a  separate  existence. 

The  sexual  reproductive  cells  lie  in  the  jelly-like  layer  of  the 


Fig.  56.  —  A  simple  sponge,  Sycon.  The 
right-hand  member  of  the  colony  is  shown  in 
longitudinal  section.  ip,  incurrent  pores; 
0,  osculum.     (From  Parker  and  Haswell.) 


PHYLUM   PORIFERA 


97 


body- wall.  Both  eggs  and  sperms  occur  in  a  single  indi\idual; 
i.e.  Grantia  is  monoecious  or  hermaphroditic.  The  development 
of  the  fertilized  egg  has  been  observed  in  Sycon  (Fig.  57)  and  is 
probably  similar  to  what  occurs  in  Grantia.     The  egg  (a)  seg- 


FiG.  57.  —  Development  of  a  simple  sponge,  Sycon.  a,  ovum ;  b,  c,  ovum 
segmented;  d,  blastula;  e,  amphiblastula;  f,  commencement  of  invagination; 
g,  gastrula  attached;  h,  i,  young  sponge.  (From  Parker  and  Haswell,  after 
Schulze.) 


98 


COLLEGE   ZOOLOGY 


ments  by  three  vertical  divisions  into  a  pyramidal  plate  of  eight 
cells  (b,  c).  A  horizontal  division  now  cuts  off  a  small  cell  from 
the  top  of  each  of  the  eight,  the  result  being  a  layer  of  eight  large 
cells  crowned  by  a  layer  of  eight  small  cells.  The  cells  now  be- 
come arranged  about  a  central  cavity,  producing  a  blastula-like 
sphere  (d).  The  small  cells  multiply  rapidly  and  develop  fiagella, 
while  the  large  cells  become  granular.  The  small  cells  are  now 
partially  grown  over  by  the  others,  forming  a  structure  called  the 
amphiblastula  (e).  The  mass  of  cells  then  becomes  disc-shaped 
by  the  pushing  in  of  the  flagellated  cells  (f).  Two  layers  are 
thus  formed  between  which  the  jelly-like  middle  layer  arises. 
The  invaginated  side  soon  becomes  attached  (g),  and  the  embryo 
lengthens  into  a  cylinder,  at  the  distal  end  of  which  an  opening, 
the  osculum,  appears  (h).  In  the  meantime,  spicules  arise  in 
the  body-wall. 

3.  The  Fresh- water  Sponge  —  Spongilla 

The  fresh-water  sponge  lives  in  ponds  and  streams  and  may 
be  found  attached  to  the  under  surface  of  rocks,  dead  leaves,  or 
sticks.  It  forms  incrustations  a  fraction 
of  an  inch  thick  or  compact  masses,  and 
is  gray  or  green  in  color.  The  structure 
of  Spongilla  is  shown  in  Figure  59,  C. 
The  canal  system  is  more  complicated 
than  that  of  either  Leucosolenia  or 
Grantia.  The  choanocytes  are  restricted 
to  flagellated  chambers  (C).  This  is  the 
rhagon  type,  and  there  are  three  distinct 
parts  to  this  system:  (i)  the  water  passes 
through  the  dermal  ostia  {DP),  and,  by 
way  of  incurrent  canals  {IN),  reaches  (2) 
a  number  of  small  chambers  (C)  lined 
with  choanocytes,  thence  it  is  carried 
through  (3)  an  excurrent  canal  {Ex)  to  the  gastral  cavity  {PG), 
and  finally  out  of  the  osculum  (0). 


Fig.  58. — Spongilla.  A 
single  gemmule,  seen  in 
section,  showing  the  thick 
wall  with  its  opening, 
and  the  central  mass  of 
germinal  cells.  (From 
Weysse,  after  a  Leuckart- 
Nitsche  wall-chart.) 


PHYLUM   PORIFERA  99 

SpongUla  and  several  marine  sponges  have  a  peculiar  method 
of  reproduction  by  the  formation  of  gemmules.  A  number  of 
germinal  cells  in  the  middle  layer  of  the  body-wall  gather  into 
a  ball  and  become  surrounded  by  protecting  spicules.  These 
gemmules  (Fig.  58)  are  formed  in  the  autumn  just  before  the 
death  of  the  adult  sponge.  In  thi>  spring  they  develop  into  new 
sponges.  They  are  of  value  in  carrying  the  race  through  a 
period  of  adverse  conditions,  such  as  the  winter  season. 

4.   Sponges  in  General 

(i)  Morphology.  —  External  Features.  —  Leucosolenia^ 
Grantia,  and  SpongUla  have  served  as  types  of  the  Phylum  Pori- 
FERA,  but  other  sponges  vary  markedly  from  these  both  in  form 
and  in  structure.  In  many  cases  the  character  of  the  object  to 
which  sponges  are  attached  causes  them  to  assume  exceedingly 
irregular  shapes,  the  rocks  being  frequently  incrusted  by  in- 
definite masses  of  spongy  tissue.  The  habit  of  growth  of  many 
sponges  is  responsible  for  their  shape.  Some  are  branched  like 
trees,  or  form  a  network;  others  are  fan-shaped,  cup-shaped, 
or  dome-shaped.  Some  sponges  are  no  larger  than  a  pinhead; 
others  are  over  five  feet  high.  Most  calcareous  sponges  are 
white  or  gray,  but  others  may  be  brilliantly  colored  and  even 
iridescent,  exhibiting  all  the  hues  of  the  rainbow. 

Canal  Systems.  —  There  are  three  principal  types  of  canal 
systems  exhibited  by  sponges:  (i)  ascon,  (2)  sycon,  and  (3) 
rhagon.  That  of  Leucosolenia  (p.  94,  and  Fig.  59,  A)  is  of  the 
ascon  type,  and  that  of  Grantia  (page  95,  and  Fig.  59,  B)  is  of  the 
sycon  type.  Some  sponges,  like  SpongUla,  have  a  very  compli- 
cated canal  system;  this,  the  rhagon  type,  is  diagrammatically 
shown  in  Figure  59,  C,  and  described  on  page  98. 

Skeletal  Systems.  —  The  skeletons  of  sponges  are  composed 
of  spicules  of  carbonate  of  lime  or  silicon,  or  of  fibers  of  spongin. 
A  few  small  species  have  no  skeletons.  Some  of  the  more  com- 
mon types  of  spicules  are  shown  in  Figure  60;  they  are  (i) 
monaxon  (a,  h) ,  X'^ rt^lrax^n,  (c,  4)1^(3)  ^'wa*i>«- (e4,;and  (4)  poly- 


lOO 


COLLEGE  ZOOLOGY 


axon  (f).     Spicules  with  three  rays  like  most  of  those  in  Leuco- 
solenia  and  Grantia  are  called  triradiate.    The  skeletons  of  the 


1 

osc 

1    ' 

1 

J^ 

1  • 

13 

i 

.1 

;.a» 

C.C 

^^  . 

IS 

\ 

J 

???*? 

/Ty  osc.  \\ 

,  Js  C.C.  ^ 


^/Zci 


c  P.f^ 


CO 


Fig.  59.  —  Types  of  canal  systems  of  sponges.  A,  Ascon  type.  B,  Sycon 
type.  C,  Rhagon  type  {Spongilla).  The  arrows  indicate  the  direction  of  the 
current  of  water.  The  thick  black  line  in  A  and  B  represents  the  gastral  layer  ; 
the  dotted  portion,  the  dermal  layer,  ap.p,  apopyle;  fl.c,  flagellated  chamber; 
GC,  gastral  cavity  (cloaca);  in.c,  incurrent  canal;  o^c,  osculum;  pr.p,  pro- 
sopyle.  C,  flagellated  chambers ;  DP,  dermal  pores ;  Ex,  excurrent  canals ; 
GO,  openings  of  excurrent  canals;  In,  incurrent  canals;  O,  osculum;  PG,  gastral 
cavity;  SD,  subdermal  cavity.  (A  and  B,  from  Minchin  in  Lankester's 
Treatise;  C,  from  Parker  and  Haswell,  after  a  Leuckart-Nitsche  wall-chart.) 

horny  sponges,  of  which  the  common  bath  sponge  is  an  example, 
are  made  up  largely  of  fibers  of  spongin  (Fig.  6i).  This  sub- 
stance, which  is  chemically  allied  to  silk,  is  secreted  by  cells  of 
the  dermai ' tayer  c^XeA^ spongoblast'S.:     ;  ,: 


PHYLUM  PORIFERA 


lOI 


Histology/— The  sponges  are  among  the  simplest  of  the 
Metazoa  with  regard  to  the  differentiation  of  their  cells,  but 
they  seem  quite  complex  when  compared  with  the  Protozoa. 


V 

Fig.  6o. — Types  of  sponge  spicules.  Fig.  6i.  —  Piece  of  net- 

a,  b,  monaxon;  c,  d,  tetraxon;  e,  triaxon;  work  of  horny  fibers  from 

f ,     polyaxon.       (From     the     Cambridge  the  bath  sponge,  Euspongia. 

Natural  History.)  (From  Sedgwick.) 

The  cells  of  sponges  may  be  separated  into  three  groups: 
(i)  those  of  the  dermal  layer,  (2)  those  of  the  gastral  layer,  and 
(3)  the  ameboid  cells  in  the  jelly  between  the  dermal  and  gastral 
layers.  The  classes  of  cells  and  the  layers  to  which  they  belong 
are  show^n  in  Table  III. 

TABLE  III 

CLASSES   OF   CELLS   FOUND  IN   SPONGES 


A.  Dermal 
Layer 


B.  Gastral 
Layer 

C.  Middle  Re- 
gion 


I.  Epithelial  stratum 

II.  Porocytes 

III.  Skeletogenous  stratum 


1.  Epithelial  cells 

2.  Contractile  cells 

3.  Gland  cells 

4.  Spongoblasts 

5.  Pore  cells 

6.  Scleroblasts 

7.  Fiber  cells 


IV.  Gastral  epithelium 

8. 

Choanocytes 

V.  Wandering  cells 

VI.  Reproductive  cells 

9- 
10. 
II. 

[12. 
13. 

Ingestive  cells 
Nutritive  cells 
Storage  cells 
Gemmule  cells 
Sexual  cells 

I02  COLLEGE  ZOOLOGY 

(2)  Physiology.  —  Metabolism.  —  The  metabolic  processes 
in  all  sponges  are  essentially  similar  to  those  of  Grantia  (p.  96). 
The  current  created  by  the  beating  of  the  flagella  of  the  choano- 
cytes  brings  organic  food  particles  and  fresh  water  into  the  canals. 
Most  of  the  food  particles  are  engulfed  by  the  choanocytes  and 
digested  within  the  cells,  as  in  Protozoa.  The  processes  of  ex- 
cretion and  respiration  are  carried  on  by  the  cells  of  the  body- 
wall.  There  is,  on  the  whole,  not  much  difference  between  the 
metabolic  activities  of  sponges  and  those  of  Protozoa. 

Behavior.  —  Very  little  is  known  about  the  behavior  of 
sponges.  The  larvae,  as  stated  before,  are  ciliated  and  swim 
through  the  water,  but  the  adults  are  all  attached  to  the  sea- 
bottom,  to  rocks,  or  to  piles,  etc.  Parker  has  shown  that  Stylo- 
tella  heliophila,  of  the  order  Monaxonida,  responds  in  a  prim- 
itive way  to  certain  stimuli.  Among  the  reacting  elements  are 
fiber-like  cells,  myocytes,  arranged  about  the  osculum,  and  con- 
tractile cells  lining  certain  internal  cavities.  The  choanocytes 
are  able  to  extend  and  contract  their  collars  and  to  beat  the  water 
with  their  flagella.     No  nervous  elements  have  been  discovered. 

The  reactions  of  Stylotella  may  be  briefly  stated  as  follows:  — 

The  oscula  close  in  quiet  sea-water,  on  exposure  to  air,  on  in- 
jury to  neighboring  parts,  and  in  weak  solutions  of  ether  and 
cocaine;  they  open  in  currents  of  sea-water,  in  fresh  water,  and 
in  weak  solutions  of  atropine. 

The  ostia  close  on  injury  to  neighboring  parts  and  in  weak 
solutions  of  ether  and  cocaine;  they  open  in  dilute  sea-water, 
and  in  weak  solutions  of  atropine.  The  choanocyte  currents 
cease  in  dilute  sea- water,  at  high  temperatures,  and  in  weak  solu- 
tions of  ether  and  chloroform.  There  is  very  little,  if  any,  trans- 
mission of  stimuli,  and  the  reactive  organs  respond  only  to 
direct  stimulation. 

Investigators  look  to  the  lowly  organized,  many-celled  animals 
for  the  key  to  the  origin  of  the  nervous  system,  and  the  condition 
in  sponges  seems  to  show  that  muscles,  "  as  represented  by  the 
sphincters  of  sponges,  were  the  first  of  the  neuromuscular  organs 


PHYLUM    PORIFERA 


103 


Fig.  62. 


Venus'  flower-basket.     The  skeleton  of  a  sponge,  Euplectella. 
(From  Weysse.) 


to  appear."  Sense  cells  are  supposed  to  have  developed  next 
as  we  find  them  in  ccelenterates  (p.  112),  and  finally  a  central 
organ  was  added,  completing  the  neuromuscular  mechanism 
as  it  exists  in  higher  Metazoa. 

(3)  Reproduction.  —  Reproduction  is  either  asexual  or  sexual. 
By  the  asexual  method  there  are  produced  biids  and  gemmules. 
Buds  may  be  set  free  to 
take  up  a  separate  existence, 
or  may  remain  attached  to 
the  parent  sponge,  aiding  in 
the  formation  of  a  complex  *^^^f:^^f^^^k^' 
assemblage  of  individuals. 
Gemmules  are  formed  as  de- 
scribed in  Spongilla  (p.  99). 

In  sexual  reproduction  the 
eggs   and   spermatozoa  are      fig.  63. -The  bath  sponge,  £«./,.«,ia 

derived  as  in  Sycon   (p.  96)    officinalis.    (From  Lankester,  after  Schulze.) 


I04  COLLEGE  ZOOLOGY 

from  ameboid  wandering  cells  in  the  middle  layer.  A  ciliated 
larva  is  produced  from  a  holoblastic  egg.  This  larva  swims 
about  for  a  while,  thus  effecting  the  dispersal 
of  the  species,  then  becomes  fixed  and  passes 
through  many  changes,  finally  developing 
ostia  and  an  osculum  which  are  necessary 
for  the  nutritive  processes  and  growth. 

One  very  important  peculiarity  in  sponge 

embryology  is  this  (Fig.  64) :  the  flagellated 

^ .  cells  of  the  larva  do  not  become  the  outer 

Fig.  64.  —  Section   (dermal)  epithelium  as  do  the  flagellated  cells 

of   the   larva   of   a  of  the  larval  coelenterate  (planula,  Fig.  73,  C, 

Uancl^'   p.gx,  'lit  ^ig-  ^i)'  but   produce  the  gastral   layer  of 

terior  granular  cells,  choanocytcs;  and  the  inner  cells  do  not  be- 

(From   Lankester's  .1        •  /        ^     i\         ^,^     ^•  i 

Treatise.)  come  the  inner   (gastral)   epithelium,  as  do 

the  similarly  situated  cells  in  the  coelen- 
terate planula,  but  produce  the  dermal  layer.  This  is  shown 
in  Table  IV. 

TABLE  IV 

THE  DEVELOPMENT   OF  A    SPONGE    (cLATHRINA) 

Flagellated  cells    .     .     .  Gastral  layer 
Ameboid  inner  cells  .     .  Dermal  layer 
Posterior  granular  cells  J  Wandering  cells 
(Fig.  64,  p.gx.)  \  Sexual  cells 


Ovum-Blastomeres 


It  therefore  seems  impossible  to  homologize  the  ectoderm  and 
entoderm  of  ccelenterates  and  other  Metazoa  with  the  layers  in 
the  sponge  larva,  since  the  outer  layer  (ectoderm?)  of  the  latter 
becomes  the  inner  layer  (entoderm?)  of 'the  adult  sponge.  The 
outer  layer  is  consequently  termed  "  dermal  epithelium  "  instead 
of  "  ectoderm,"  and  the  inner,  the  "  gastral  epithelium  "  instead 
of  "  entoderm." 

(4)  Classification.  —  Porifbra.  —  Sponges.  —  Diploblastic, 
radially  symmetrical  animals;  number  of  antimeres  variable; 
body- wall  permeated  by  many  pores,  and  usually  supported  by  a 
skeleton  of  spicules  or  spongin. 


PHYLUM   PORIFERA  1 05 

Class  I.  Calcarea.  Marine  species,  mostly  white  or  gray, 
living  in  shallow  water;  spicules  of  carbonate  of  lime,  either 
monaxon  (Fig.  60,  a,  b)  or  tetraxon  (Fig.  60,  c,  d.) ;  flagellated 
chambers  large. 

Order  i.  Homocoela.  Gastral  layer  continuous.  Example: 
Leucosolenia  (Fig.  52,  Fig.  59,  A).    , 

Order  2.  Heteroccela.  Gastral  layer  discontinuous  and  re- 
stricted to  flagellated  chambers.  Example:  Grantia  (Fig.  55, 
Fig.  59,  B). 

Class  II.  Hexactinellida.  Deep-sea  sponges ;  spicules 
triaxon  (Fig.  60,  e),  of  silicon;  canal  system  with  thimble-shaped 
chambers.  Example:  Euplectella  aspergillum,  Venus'  flower- 
basket  (Fig.  62). 

Class  III.  Demospongle.  Skeleton  of  silicious  spicules, 
not  triaxon,  or  with  spongin,  or  with  both  spicules  and  spongin, 
canal  system  derived  from  rhagon  type  (Fig.  59,  C) ;  most  highly 
organized  of, phylum;  majority  of  existing  sponges. 

Order  i.  Tetraxonida.  Typically  with  tetraxon  spicules. 
Example:  Geodia. 

Order  2.  Monaxonida.  With  monaxon  (Fig.  60,  a,  b),  but 
no  tetraxon  spicules  (c,  d).     Example:  Spongilla  (Fig;  59,  C). 

Order  3.  Keratosa.  Main  skeleton  of  spongin.  Example: 
Euspongia,  the  bath  sponge  (Fig.  63). 

(5)  The  Position  of  Sponges  in  the  Animal  Kingdom.  —  As 
stated  at  the  beginning  of  this  chapter,  sponges  are  considered 
many-celled  animals.  They  were  formerly,  and  are  even  now, 
placed  by  some  authors  in  a  phylum  with  the  coelenterates 
(Chapter  V).  They  differ  from  the  ccelenterates  and  other 
Metazoa  so  widely  in  certain  important  characteristics  that 
most  zoologists  are  inclined  to  separate  them  from  the  Metazoa 
and  call  them  Parazoa  (see  diagram,  p.  25). 

Sponges  differ  from  coelenterates  in  the  presence  of  choano- 
cytes,  ostia,  and  oscula,  in  their  unique  method  of  feeding,  in  the 
germ-layers,  which  are  apparently  reversed  in  position  (p.  104), 
and  in  the  absence  of  a  mouth  and  nematocysts  (Fig.  66).     The 


lo6  COLLEGE  ZOOLOGY 

choanocytes  of  sponges  recall  the  choanoflagellate  Protozoa 
(p.  47),  and  it  is  not  improbable  that  they  may  have  evolved 
from  this  group.  Certain  colonial  choano flagellates,  e.g.  Protero- 
spongia  (P'ig.  29)  resemble  what  we  might  imagine  to  have  been 
the  ancestor  of  the  sponges. 

(6)  The  Relations  of  Sponges  to  Other  Organisms  and  to  Man.  — 
Sponges  are  used  as  food  by  very  few  animals,  since  they  are  pro- 
tected by  spicules  and  by  excretions  of  poisonous  ferments  mak- 
ing them  distasteful.  Nudibranch  mollusks  (Chap.  XII)  feed 
on  them  to  a  certain  extent.  The  cavities  of  sponges  offer  shel- 
ter to  many  animals,  especially  Crustacea  and  coelenterates; 
this  may  lead  to  a  sort  of  partnership  called  commensalism.  For 
example,  certain  hermit  crabs  protect  themselves  from  attack 
by  surrounding  their  shells  with  obnoxious  sponges.  Oysters 
and  other  bivalves  are  often  starved  by  sponges  which  cover 
their  shells  and  take  away  their  food  supply,  and  oyster  cultur- 
ists  often  prevent  this  by  growing  the  bivalves  in  frames  which 
are  pulled  up  during  a  rain,  thus  killing  the  sponges  with  fresh 
water. 

The  origin  of  flint  is  in  part  due  to  the  activities  of  sponges. 
It  has  been  estimated  that  to  extract  one  ounce  of  silicious  spicules 
at  least  a  ton  of  sea  water  must  pass  through  the  canal  system 
of  the  sponge.  The  spicules  aid  in  the  formation  of  flint,  this 
substance  being  always  associated  with  the  remains  of  sponges, 
Radiolaria  (p.  40),  and  other  organisms  having  silicious  skele- 
tons. 

Of  the  commercial  sponges  may  be  mentioned  the  beautiful 
skeleton  of  Venus'  flower-basket,  Euplectella  (Fig.  62),  which 
is  obtained  chiefly  in  the  Philippine  Islands,  and  the  common 
bath  sponge,  Euspongia  (Fig.  63),  and  others,  which  are  especially 
grown  for  market  in  some  localities.  The  best  bath  sponges 
come  from  the  Mediterranean  coast,  Australia,  the  Bahamas, 
Florida,  and  the  north  coast  of  Cuba.  They  are  gathered  by 
means  of  long  hooks,  by  divers,  or  by  dredging.  They  are  al- 
lowed to  decay,  are  washed,  dried,  and  then  sent  to  market. 


PHYLUM   PORIFERA  107 

The  depletion  of  the  sponge  supply  by  unwise  fishing  has  re- 
sulted in  an  attempt  to  regulate  the  industry  by  governmental 
control.  Sponge  culture  is  now  carried  on  successfully  in  Italy 
and  Florida.  Perfect  specimens  are  cut  into  pieces  about  one 
inch  square,  and  "  planted  "  on  stakes  on  clean,  rocky  bottoms 
free  from  cold  currents.  These  grow  into  marketable  size  in 
five  or  six  years. 


CHAPTER   V 
PHYLUM    CCELENTERATA 

The  Phylum  Cgelenterata  (Gr.  koilos,  hollow;  enteron, 
intestine)  includes  a  great  number  of  aquatic  animals,  mostly 
marine,  very  few  of  which  ever  come  to  the  notice  of  persons 
who  do  not  visit  the  sea-shore  or  are  not  especially  interested  in 
natural  history.  As  in  the  case  of  the  sponges,  many  species 
of  coelenterates,  the  corals,  are  known  because  of  the  beautiful 
skeletons  they  construct. 

The  three  classes  of  coelenterates  are  as  follows:  — 

Class  I.  Hydrozoa  (Gr.  hudra,  a  water  serpent;  zoon,  an 
animal),  fresh- water  polyps,  hydroid  zoophytes,  many  of  the 
small  medusae  or  jelly  fishes,  and  a  few  stony  corals; 

Class  II.  Scyphozoa  (Gr.  skuphos,  cup;  zoon,  animal),  most 
of  the  large  jelly  fishes;   and 

Class  HI.  Anthozoa  (Gr.  anthos,  a  flower;  zoon,  animal), 
(Actinozoa),  sea-anemones,  most  stony  corals,  sea-fans,  sea-pens, 
and  precious  corals. 

A  simple  member  of  the  Ccelenterata  and  one  that  is  com- 
mon in  fresh  water  is  the  polyp  known  as  Hydra.  A  study 
of  this  little  animal  will  serve  to  illustrate  coelenterate  charac- 
teristics and  will  enable  one  to  understand  the  more  complex 
species  belonging  to  this  phylum. 

I.  The  Fresh- water  Polyp  —  Hydra 

Hydra  fusca  is  abundant  in  ponds  and  streams,  where  it  may 
be  found  attached  by  one  end  to  aquatic  vegetation.  Hydras 
are  easily  seen  with  the  naked  eye,  being  from  2  to  2Q_iQm.  in_ 

108 


PHYLUM   CCELENTERATA  109 

length.     They  may  be  Ukened  to  a  short,  thick  thread  unraveled 
"ai'tlTe  unattached,  distal  end. 

Morphology.  —  External  Features.  —  The  body  of  Hydra 
is  really  a  tube  usually  attached  \)y  a  hasal  ^isj^jit  one  end,  and 
with  a  mouth  opening  at  the  distal  or  free  end.  ^roundJLhe 
mouth  are  arrangecjirom  six  to  te^i  smaller  tubes,  closed  at  their 
outer  end,  called  tenlacles  (Fig.  65,  t).  Both  the  body  and  ten- 
tacles vary  at  different  times  in  length  and  thickness.  One  or 
more  buds  (Fig.  65,  h)  are  often  found  extending  out  from  the 
body,  and  in  September  and  October  reproductive  organs  may 
also  appear.  The  male  organs  {testes,  Fig.  65,  y.t,  m.t)  are  con- 
ical elevations  on  the  distal  third  of  the  body;  the  female  organs 
{ovaries,  Fig.  65,  y.e,  m.e)  are  knoblike  projections  near  the 
basal  disc. 

Structure  (Fig.  65).  —  Hydra  is  a  ^j-bli^hlastic  animal  con- 
sisting of  two  cellular  layers,  an^^u^thin,  colorless  layer,  the 
ectoderm  {ec.)  and  an  iim^r  layer,  the  entoderm  {en),  twice  as 
thick  as  the  outer,  and  containing  the  brown  bodies  which  give 
Hydra  fusca  its  characteristic  color.  Both  layers  are  composed 
of  ^^H^glioidilii'  ^  thin  space  containing  a  non-cellular  jelly- 
like substance,  the  nieso^lea  {mes.),  separates  ectoderm  from 
entoderm.  Not  only  the  body-wall,  but  also  the  tentacles,  pos- 
sess these  three  definite  regions.  The  body,  with  the  exception 
of  the  basal  disc,  is  covered  by  a  thin,  transparent  cuticle.  Both 
body  and  tentacles  areJi^Haffi,  the  single  central  space  being 
known  as  the  ^astrovascular  cavity  {gv.c). 

The  ectoderm  is  primarily  protective  and  sensory,  and  is  made^\ 
up  of  two  principal  kinds  of  cells:  (i)  epitheliomuscular,  and  (2)  ^ 
interstitial.     The  former  are  shaped  like  inverted  cones,  and  pos- 
sess long  (up  to  .38  mm.),  unstriped  contractile  fibrils  at  their 
inner  ends;  these  enable  the  animal  to  expand  and  contract.      "~\ 

The  interstitial  cells  lie  among  the  bases  of  the  epitheliomuscular    \ 
cells;    they  give  rise  to  three  kinds  of  nematocvsts  or  stinging     J 
cells  (Fig.  65,  w;  Fig.  66).     Nematocysts  are  present  on  all  parts 
of  the  body  except  the  basal  disc,  being  most  numerous  on  the 


no 


COLLEGE  ZOOLOGY 


tentacles.  The  interstitial  cell  in  which  the  nematocyst  develops 
is  called  a  cnidoblast  (Fig.  66);  it  contains  a  nucleus  (nu)  and 
develops  a  trigger-like  process,  the  cnidocil  (cnc),  at  its  outer  end, 


Fig.  65.  —  Diagram  of  a  longitudinal  section  of  Hydra,  b,  bud;  b.d,  basal 
disc;  hi,  blastula;  ec,  ectoderm;  en,  entoderm;  g,  gastrula;  gv.c,  gastro- 
vascular  cavity;  hy,  hypostome;  m,  mouth;  m.e,  mature  egg;  mJ,  mature  testis; 
n,  nematocysts;  p.b,  polar  bodies;  /,  tentacle;  y.e,  young  egg;  y.  t,  young  testis. 
All  the  structures  shown  do  not  occur  on  a  single  animal  at  one  time. 


but  is  almost  completely  filled  by  the  pear-shaped  nematocyst 
(nem).  Within  this  structure  is  an  inverted  coiled  thread-like 
tube  with  barbs  at  the  base.     When  the  nematocyst  explodes, 


PHYLUM   CCELENTERATA 


III 


this  tube  turns  rapidly  inside  out  and  is  able  to  penetrate  the 
tissues  of  other  animals  (Fig.  67,  B;  Fig.  68,  A).  The  explosion 
is  probably  due  to  internal  pressure  produced  by  osmosis,  and 
may  be  brought  about  by  various  methods  such  as  the  application 
of  a  little  acetic  acid  or  methyl  green.  Many  animals  when 
"  shot  "  by  nematocysts  are  immediately  paralyzed  and  some- 
times killed  by  a  poison  called  hypno- 
toxin  which  is  injected  into  it  by  the 
tube. 

Two  kinds  of  nematocysts  smaller 
than  that  just  described  are  also  found 
in  the  ectoderm  of  Hydra.  One  of 
these  is  cylindrical  and  contains  a 
thread  without  barbs  at  its  base;  the 
other  is  spherical  and  contains  a  barb- 
less  thread  which,  when  discharged, 
aids  in  the  capture  of  prey  by  coiling 
around  the  spines  or  other  structures 
that  may  be  present  (Fig.  68,  B). 

Certain  ectoderm  cells  of  the  basal 
disk  of  Hydra  are  dandular  and  secrete 
a  sticky  substance  for  the  attachment 
of  the  animal. 

The  entoderm ,  the  inner  layer  of 
cells,  is  primarily  digestive,  absorptive, 
and  secretory.  The  digestive  cells  are 
large,  with  muscle  fibrils  at  their  base, 
and   fiagella   or   pseudopodia  at   the 

end  which  projects  into  the  gastrovascular  cavity.  The  fiagella 
create  currents  in  the  gastrovascular  fluid,  and  the  pseudopodia 
capture  solid  food  particles.  The  glandular  cells  are  small  and 
without  muscle  fibrils.  Interstitial  cells  are  found  lying  at  the 
base  of  the  other  entoderm  cells. 

The  mesodea  is  an  extremely  thin  layer  of  jelly-like  substance 
situated  between  the  other  two  layers. 


Fig.  66.  —  Nematocysts  of 
Hydra  before  and  after  dis- 
charge, cnc,  cnidocil ;  nem, 
nematocyst;  nu,  nucleus  of 
cnidoblast;  /,  thread-like  tube. 
(From  Dahlgren  and  Kepner, 
after  Schneider.) 


112 


COLLEGE  ZOOLOGY 


From  recent  investigations  it  seems  well  established  that 
Hydra  possesses  a  nervous  system,  though  complicated  staining 
methoos  are  necessary  to  make  it  visible.  In  the  ectoderm  there 
is  a  sort  of  plexus  of  nerve-cells  connected  by  nerve- fibers  with 
centers  in  the  region  of  the  mouth  and  foot.  Sensory  cells  in 
the  surface  layer  of  cells  serve  as  external  organs  of  stimulation, 
and  are  in  direct  continuity  with  fibers  from  the  nerve  cells. 
Some  of  the  nerve-cells  send  processes  to  the  muscle  fibers  of 


Fig.  67.  —  Nematocysts  of  Hydra 
and  their  action.  A,  portion  of  a  ten- 
tacle showing  the  batteries  of  nemato- 
cysts ;  cl,  cnidocils.  B,  insect  larva 
covered  with  nematocysts  as  a  result  of 
capture  by  Hydra.      (From  Jennings.) 


Fig.  68.  —  The  action  of 
nematocysts.  A,  a  nematocyst 
piercing  the  chitinous  covering 
of  an  insect.  B,  nematocysts 
holding  a  small  animal  by  coil- 
ing about  its  spines.  (After 
Toppe  in  Zool.  Anz.) 


the  epitheliomuscular  cells,  and  are  therefore  motor  in  function. 
No  processes  from  the  nerve-cells  to  the  nematocysts  have  yet 
been  discovered,  though  they  probably  occur.  The  entoderm 
of  the  body  also  contains  nerve-cells,  but  notj  so  manv_as  are 
present  in  the  ectoderm. 
f  Physiology.  —  Nutrition.  —  Hydra  lives  on  minute  aquatic 
animals  which  come  w^ithin  reach  of  its  tentacles.  The  nemato- 
cysts, and  probably  a  secretion  from  the  tentacles,  paralyze 
the  prey,  while  the  viscid  surface  of  the  tentacle  prevents  it 


PHYLUM   CCELENTERATA  1 13 

from  escaping.     Food  is  carried  to  the  mouth  by  the  bending 
over  of  the  tentacle  which  captured  it;  other  tentacles  also  assist. 
The  mouth  opens  and  slowly  moves  around  the  food,  which  is 
then  forced  down  to  the  basal  end  of  the  gastrovascular  cavity  \ 
by  the  contraction  of  the  body- wall  behind  it.  J 

Hydras  will  not  capture  prey  oi^  respond  to  food  stimuli  when 
they  have  recently  been  fed.  Moderately  hungry  specimens 
will  exhibit  the  characteristic  food-taking  reactions  if  both 
chemical  and  physical  stimuli  are  applied  at  the  same  time,  e.g., 
a  piece  of  filter  paper  soaked  in  beef  juice.  A  hungry  animal 
will  respond  by  making  swallowing  movements  when  a  chemical 

stimulus  alone  is  applied.  

^DieesUpntakes  place  in  the  gastrovascular  cavity  and  probably  ( 
also  within  the  entoderm  cells.     The  gland  cells  of  the  entoderm  \ 
secrete  a  fluid  into  the  gastrovascular  cavity;  this  fluid  dissolves 
the  food.     Digestion  is  aided  by  the  currents  set  up  by  the 
flagella  of  the  entoderm  cells  and  by  the  churning  resulting  from 
the  expansion  and  contraction  of  the  body.     Part  of  the  food 
is  evidently  engulfed  by  the  pseudopodia  of  the  entoderm  cells 
and  undergoes  ^^itottdWfflli  digestion.     The  dissolved  food  is 
ahsor^^pd  by  the  entoderm  cells;  part  of  it,  especially  the  oil  glob- 
ules, is  passed  over  to  the  ectoderm,  where  it  is  stored   untilj 
needed. 

Behavior.  —  Hydras  are  usually  found  attached  to  the  bot- 
tom or  sides  of  the  aquarium,  or  to  aquatic  plants,  or  are  sus- 
pended from  the  surface  film  of  the  water.  The  position  of  rest,] 
with  the  body  stretched  out  and  the  tentacles  widely  spread, 
allows  the  animal  to  obtain  food  from  a  considerable  area.  At 
intervals  of  several  minutes -an  undisturbed  Hydra,  especially  if 
hungry,  will  cjaptract  rapidly  and  then  slowly  expand  in  a  new 
direction,  as  shown  in  Fig.  69.  This  brings  it  into  a  new  part  of 
its  surroundings,  where  more  food  may  be  present.  Finally, 
these  spontaneous  movements  cease,  and  the  animal  moves  to 
another  place. 

Locomotion  is  known  to  be  effected  in  three  ways.     Usually 


114 


COLLEGE  ZOOLOGY 


the  animal  bends  over  (Fig.  70,  i)  and  attaches  itself  to  the  sub- 
stratum by  its  tentacles  (2) ;  the  basal^  disc  is  then  released  and 
the  animal  contracts  (j) ;  the  body  then  expands  {4) ,  bends  over 
in  some  other  direction  and  becomes  attached  (5) ;  finally  the 
tentacles  are  released  and  an  upright  position  is  regained  (6). 


Fig.  69.  —  Spontaneous  changes  of  positions  in  an  undisturbed  Hydra. 
Side  view.  The  extended  animal  (i),  contracts  (2),  bends  to  a  new  position  (3), 
and  then  extends  (4).     (From  Jennings.) 


This  method  of  locomotion  has  been  compared  to  that  of  the 
measuring-worm.  At  other  times  the  animal  uses  its  tentacles 
asjegs,  or  gUdes  along  on  its  basal  disc. 

C"  Hydras  react  to  mechanical  stimulation,  to  light,  temperature, 
and  electricity.  If  a  watch-glass  containing  a  specimen  is  jarred, 
or  the  surface  of  the  water  agitated,  a  part  or  all  of  the  body  and 
tentacles  contract;  this  is  the  result  of  a  non-localized  mechanical 
stimulus.  If  the  body  or  a  tentacle  is  touched  with  a  glass  rod, 
the  body  or  tentacles  contract,  depending  on  the  strength  of  the 
stimulus. 

Changes  in  the  intensity  of  the  light  cause  Hydras  to  move 


PHYLUM    CCELENTERATA 


"5 


about  until  they  reach  a  region  where  the  light  is  most  favorable; 
this  may  be  called  their  optimum.  They  find  this  optimum 
by  the  method  of  ''  trial  and  error/'  i.e.  their  movements  are  in- 
definite, all  directions  bemg  tried  until  the  proper  conditions  are 
encountered.  In  a  well-lighted  area  they  are  most  likely  to 
secure  the  small  animals  that  sen^ 
as  food,  since  these  are  also  attracted 
by  light. 

When  subjected  to  heat,  th^^^j^ 
and  error  mgttiad  is  likewise  em- 
ployed; the  animals  escape  if  they 
chance  to  move  into  a  cooler  area, 
but  perish  if  they  remain  in  a  heated 
region  too  long. 

p^The  reactions  of  a  hungry  Hydra 
\to  food  indicate  that  the  physio- 
logical condition  of  the  animal  de- 
termines to  a  large  extent  the  kind 
[of  reactions  produced,  not  only 
spontaneously,  but  also  by  external 
stimuli.  "  It  decides  whether  Hydra 
shall  creep  upward  to  the  surface 
and  toward  the  light,  or  shall  sink 
to  the  bottom;   how  it  shall  react 

to  chemicals  and  to  solid  objects;  whether  it  shall  remain  quiet 
in  a  certain  position,  or  shall  reverse  this  position  and  undertake 
a  laborious  tour  of  exploration." 

C  Reproduction. — Hydra  reproduces  asexually  by  budding  and  by 
fission,  and  sexually  by  the  production  of  eggs  and  spermatozoa. 
Budding  (Fig.  65,  b)  is  quite  common,  and  may  easily  be  ob- 
served in  the  laboratory.  The  bud  appears  first  as  a  slight  bulge 
in  the  body- wall.  This  pushes  out  rapidly  into  a  stalk,  which 
soon  develops  a  circlet  of  blunt  tentacles  about  its  distal  end. 
The  cavities  of  both  stalk  and  tentacles  are  at  all  times  directly 
connected  with  that  of  the  parent.     When  full  grown,  the  bud 


Fig.  70.  —  Hydra  moving  like 
a  measuring  worm.  (From  Jen- 
nings, after  Wagner.) 


ii6 


COLLEGE  ZOOLOGY 


u 


\  ^SM 


becomes  detached  and  leads  a  separate  existence.  Sometimes 
the  bud  may  begin  to  form  other  buds  before  it  becomes  de- 
tached from  the  parent  animal  In  this  way  a  sort  of  hydroid 
colony  is  produced  resembling  that  of  certain  marine  ccelenterates 
like  Ohelia  (Fig.  73).  F^.y.v^'g^  is  less  coijj^^|^|j^.  The  distal  end 
of  the  animal  divides  first;  then  the  body  slowly  splits  down  the 
center,  the  halves  finally  separating  when  the  basal  disc  is  sev- 
ered (Fig.  71).  Hydras  have  also  been  found  which  bore  buds 
reproducing  in  this  manner.    This  method  of  multiplication  must, 

however,  be  rare,  since  it  is  so 
seldom  seen.  Transverse  fission 
has  also  been  reported. 

The   processes  concerned   in 

^Pri^nl  rppYndurfigfi.  are  the  pro- 

\  duction  of  spermatozoa  and 
eggs,  the  fertilization  of  the  egg, 
the  development  and  hatching 
of  the  embryo,  and  the  growth 
of  the  young  larva.  The  sper- 
matozoa arise  in  the  testis  from 
ectodermal  interstitial  cells 
(Fig.  65,  y.t.) ;  they  develop  in 
long  cysts  (Fig.  65,  m.t.)  through  the  end  of  which  they  escape 
into  the  surrounding  water.  The  eggs  arise  in  the  ovary  from 
ectodermal  interstitial  cells  (Fig.  65,  y.e.).  Usually  only  one 
egg  develops  in  a  single  ovary.  When  a  certain  period  of 
growth  is  reached,  two  polar  bodies  (Fig.  65,  p.b.)  are  given  off  by 
the  egg,  which  is  then  said  to  be  mature  (Fig.  65,  m.e.).  Fer- 
tilization occurs  usually  within  two  hours  after  the  polar  bodies 
have  been  formed. 

The  cleavage  of  the  egg  is  total  and  almost  equal,  a  bias  tula 
(Fig.  65,  bl)  being  formed  with  a  distinct  cavity,  the  blastoccel. 
A  solid  gastrula-like  structure  (Fig.  65,  g)  is  produced  by  the 
filling  up  of  the  blastoccel  with  cells  budded  off  from  the  blas- 
tula  wall.     The  outer  cells  may  be  called  ectoderm  and  the  inner 


Fig.  71.  —  Hydra  reproducing  by 
longitudinal  fission.  (After  Koelitz  in 
Zool.  Anz.) 


PHYLUM   CCELENTER.A.TA 


117 


cells  entoderm.  The  ectoderm  now  secretes  a  thick  chitinous 
shell  covered  with  sharp  projections.  The  embryo  then  separates 
from  the  parent  and  falls  to  the  bottom,  where  it  remains  un- 
changed for  several  weeks.  Then  interstitial  cells  make  their 
appearance.  A  subsequent  resting  period  is  followed  by  the 
breaking  away  of  the  outer  chitinous  envelope  and  the  elongation 
of  the  escaped  embryo. 
Mesoglea  is  now  secreted 
by  the  ectoderm  and 
entoderm  cells;  a  circlet 
of  tentacles  arises  at 
one  end,  and  a  mouth 
appears  in  their  midst. 
The  young  Hydra  thus 
formed  soon  grows  into 
the  adult  condition. 

Regeneration.  —  An 
account  of  the  phe- 
nomenon of  regenera- 
tion is  appropriate  at 
this    place,    since 


Fig. 


72. — Regeneration     and     grafting     in 
the    Bydra.     A,  seven-headed  Hydra  made  by  split- 

tting  distal  ends  lengthwise.  B,  a  piece  of  Hydra 
ver  of  animals  to  regenerating  an  entire  animal.  C,  part  of  one 
:ore  lost  parts  was  Hydra  grafted  upon  another.  (From  Morgan, 
"  1  •     TT    T        ^'  after  Trembley;    B,  after  Morgan;    C,  after 

t  discovered  in  Hydra  King.) 
Trembley  in  1744. 
This  investigator  found  that  if  Hydras  were  cut  into  two, 
three,  or  four  pieces,  each  part  would  grow  into  an  entire 
animal.  Other  experimental  results  obtained  by  Trembley  are 
that  the  hypostome,  together  with  the  tentacles,  if  cut  off,  may 
produce  a  new  individual;  that  each  piece  of  a  Hydra  split  longi- 
tudinally into  two  or  four  parts,  becomes  a  perfect  polyp,  and 
that  when  the  head  end  is  split  in  two  and  the  parts  separated 
slightly,  a  two-headed  animal  results  (Fig.  72,  A). 

Q Regeneration  may  be  defined  as  the  replacing  of  an  entire 
^anism  by  a  part  of  the  same.  I    It  takes  place  not  only  in 


Il8  COLLEGE  ZOOLOGY 

Hydra,  but  in  many  other  coelenterates,  and  in  some  of  the  rep- 
resentatives of  almost  every  phylum  of  the  animal  kingdom. 
Hydra,  however,  is  a  species  that  has  been  quite  widely  used 
for  experimentation.  Pieces  of  Hydra  that  measure  \  mm.  or 
more  in  diameter  are  capable  of  becoming  entire  animals  (Fig. 
72*,  B).  The  tissues  in  some  cases  restore  the  lost  jDarts  by  a  mul- 
tiplication of  their  cells;  in  other  cases,  they  are  worked  over 
directly  into  a  new  but  smaller  individual.  Parts  of  one  Hydra 
may  easily  be  grafted  upon  another  (Fig.  72,  C).  In  this  way 
many  bizarre  effects  have  been  produced. 

Space  will  not  permit  a  detailed  account  of  the  many  interesting 
questions  involved  in  the  phenomenon  of  regeneration,  but  enough 
r~lias  been  given  to  indicate  the  nature  of  the  process.     The  benefit 
j    to  the  animal  of  the  ability  to  regenerate  lost  parts  is  obvious. 
Such  an  animal,  in  many  cases,  will  succeed  in  the  struggle  for 
existence  under  adverse  conditions,  since  it  is  able  to  regain  its 
normal  condition  even  after  severe  injuries.     Physiological  re- 
generation takes  place  continually  in  all  animals;   for  example, 
new  cells  are  produced  in  the  epidermis  of  man  to  take  the  place 
I   of  those  that  are  no  longer  able  to  perform  their  proper  functions. 
j       Both  internal  and  external  factors  have  an  influence  upon  the 
L  i;ate  of  regeneration  and  upon  the  character  of  the  new  part. 
Temperature,  food,  light,  gravity,  and  contact  are  some  of  the 
external  factors.     In  man,  various  tissues  are  capable  of  regen- 
eration; for  example,  the  skin,  muscles,  nerves,  blood-vessels,  and 
bones.     Lost  parts  are  not  restored  in  man  because  the  growing 
tissues  do  not  coordinate  properly.    Many  theories  have  been 
advanced  to  explain  regenerative  processes,  but  none  has  gained 
sufficient  acceptance  to  warrant  its  inclusion  here. 

2.   Class  I.    Hydrozoa 

Hydra  is  the  Hydrozoon  which  is  most  easily  obtained  for 
study,  and  by  means  of  Hydra  the  principal  characteristics  of  the 
coelenterates  have  been  illustrated.  There  are,  however,  a  vast 
number  of  related  animals  that  differ  widely  in  form,  structure, 


PHYLUM   CCELENTERATA  1 19 

and  habits.  The  two  chief  shapes  assumed  by  the  Hydrozoa  are 
the  hydroid,  or  polyp,  like  Hydra  and  Obelia  (Fig.  73),  and  the 
jellyfish,  or  medusa,  Uke  Gonionemus  (Fig.  74).  There  are  many 
variations  of  each  of  these,  and  frequently  one  species  may  ex- 
hibit both  conditions  at  different  periods  in  its  life-history. 

a.   A  Colonial  Hydroi^oon  —  Obelia  ^ 

Obelia  (Fig.  73)  is  a  colonial  coelenterate  which  lives  in  the 
sea,  where  it  is  usually  attached  to  rocks,  to  wharves,  or  to  Lami- 
naria,  Rhodyfnenia,  and  other  algae.  It  may  be  found  in  low 
water  and  to  a  depth  of  forty  fathoms  along  the  coast  of  northern 
Europe  and  from  Long  Island  Sound  to  Labrador. 

Anatomy  and  Physiology.  —  An  Obelia  colony  consists  of  a 
basal  stemj  the  hydrorhiza,  which  is  attached  to  the  substratum; 
this  gives  off  at  intervals  upright  branches,  known  as  hydzocauli. 
At  every  bend  in  the  zigzag  hydrocaulus  a  side  branch  arises. 
The  stem  of  this  side  branch  is  ringed  and  is  expan HeH  at  the 
end  into  a  hydra-lik^  structure,  the Jtydraigh  (Fig.  73,  A).  A 
single  polyp  consists  of  a  hydranth  and  the  part  of  the  stalk  be- 
tween the  hydranth  and  the  point  of  origin  of  the  preceding 
branch.  Full-grown  colonies  usually  bear  reproductive  members 
(gonangia)  in  the  angles  where  the  hydranths  arise  from  the  hy- 
drocaulus  (Fig.  73,  A,  S,  g,  10). 

The  Obelia  colony  as  just  described  and  as  shown  in  Fig.  73,  A, 
resembles  the  structure  that  would  be  built  up  by  a  budding 
Hydra  if  the  buds  were  to  remain  attached  to  the  parent  and  in 
turn  produce  fixed  buds. 

All  of  the  soft  parts  of  the  Obelia  colony  are  protected  by  a 
chitinous  covering  called  the  p^j;is%f  fFig.  73,  A,  6);  this  is 
ringed  at  various  places  and  is  expanded  into  cup-shaped  hydro- 
iheccp,  (Fig.  73,  A,  7)  to  accommodate  the  hydranths,  and  into 
S^onotJieccB  (Fig.  73,  A,  10)  to  inclose  the  reproc^uctiv^  membprs. 
A  shelf  which  extends  across  the  base  of  the  hydrotheca  serves 
to  support  the  hydranth.  The  soft  parts  of  the  hydrocaulus 
^  Campanularia  is  similar  to  Obelia  in  most  respects. 


I20 


COLLEGE  ZOOLOGY 


and  of  the  stalks  of  the  hydranths  constitute  the  coengsarc  (Fig. 
73,  A,  5),  and  are  attached  to  the  perisarc  by  minute  projections. 
The  ccenosarcal  cavities  of  the  hydrocaulus  open  into  those  of 


Fig.  73.  —  Hydrozoa.  A,  part  of  a  colonial  species,  Obelia.  i,  ectoderm; 
2,  entoderm;  3,  mouth;  4,  coelenteron;  5,  ccenosarc;  6,  perisarc;  7,  hydro- 
theca;  8,  blastostyle;  q,  medusa-bud;  10,  gonotheca.  B,  free-swimming 
medusa  of  Obelia.  i,  mouth;  2,  tentacles;  3,  reproductive  organs;  4,  radial 
canals;  5,  statocyst.  C,  larva  (planula)  of  Laomedea.  (A,  from  Parker  and 
Haswell;   B,  from  Shipley  and  MacBride;    C,  from  Parker,  after  AUman.) 

the  branches  and  thence  into  the  hydranths,  producing  in  this 
way  a  common  gastrovascular  cavity. 

A  longitudinal  section  of  a  hydranth  and  its  stalk  (Fig.  73,  A, 
I  to  7)  shows  the  ccenosarc  to  consist  of  two  layers  of  cells — - 


PHYLUM   CCELENTERATA  I2I 

ar^  outer  layer,  the  ectoderm,  and  an  inner  layer,  the  entoderm. 
These  layers  are  continued  into  the  hydranth  (Fig.  73,  A,  /  and 
2).  ThejmmtAisX^^  situated  in  the  center  of  the  large  knob- 
like, ^j/^o^/o  we,  and  the  tentacleSy  about  thirty  in  number,  are 
arranged  around  the  base^  of  the  hypostome  in  a  single  circle. 
Each  tentacle  is  solid,  consisting  of  an  outer  layer  of  ectoderm 
cells  (7)  and  a  single  axial  row  of  entoderm  cells;  at  the  extrem- 
ity are  a  large  number  of  nematocysts.  The  hydranth  captures, 
ingests,  and  digests  food  as  in  Hydra. 

The  reproductive _ members  arise,  as  do  the  hydranths,  as  buds 
from  the  hydrocaulus^and  represent  modified  hydranths  (Fig. 
73,  8^  p,  10).  The  central  axis  of  each  is  called  a  blastostvle  (8). 
and  together  with  the  gonothecal  covering  is  known  as  the 
gonangium.  ..J^Qj)ld^tQst^<^^vesjis.^XQjm  (Fig.  73 , 

p)  which  soon  become  detached  (Fig.  73,  B)  and  pass  out  of 
the  gonotheca  through  the  opening  in  the  distal  end. 

Some  of  the  medusce  of  Ohelia  (Fig.  73,  B)  produce  eggs,  and 
others  produce  spermatozoa.  The  fertilized  eggs  develop  into 
colonies  like  that  which  gave  rise  to  the  medusae.  The  medusae 
provide  for  the  dispersal  of  the  species,  since  they  swim  about 
in  the  water  and  establish  colonies  in  new  habitats.  The 
structure  of  a  medusa  (Gonionemus)  will  be  described  in  sec- 
tion c  of  this  chapter.  The  medusa  of  Obelia  is  shown  in  Figure 
73,  B;   it  is_shaped.iike,jj]Mimbrdla  m 

(2)  and  a  number  of  organs  of  equilibrium  (5)  on  the  edge. 
Hanging  down  from  the  center  is  the  manubrium  (/)  with  the 
mouth  aLihe^-end ,  The  gastro\-ascular  ca\ity  extends  out  from 
the  cavity  of  the  manubrium  into  four  radial  ctuials  {4)  on  which 
are  situated  the  reproducti\  e  organs  (j). 

The  germ-cells  of  the  nudusci-  of  Obelia  arise  in  the  ectoderm 
of  the  manubrium,  and  then  migrate  along  the  radial  canals  to 
the  reproductive  organs.  When  mature,  they  break  out  into 
the  water.  The  eggs  are  fertilized  by  spermatozoa  which  have 
escaped  from  other  medusae.  Cleavage  is  similar  to  that  of 
Hydra,  and  a  hollow  blastula  and  solid  gastrula-like  structure  are 


122  COLLEGE  ZOOLOGY 

formed.  The  gastrula-like  structure  soon  becomes  ciliated  and 
elongates  into  a  free-swimming  larva  called  ci^lq^^lg{Fi^.  73,  C). 
This  soon  acquires  a  central  cavity,  becomes  fixed  to  some  object, 
and  proceeds  to  found  a  new  colony. 

b.   Metagenesis 

Metagenesis  is  the  alternation  of  a  generation  which  repro-- 
duces  Qnly  asexually  by  division  or  budding  with  a  generation 
which  reproduces  only  sexually  by  mean^  of  eggs  and  spermato- 
zoa. 'This  phenomenon  occurs  in  other  groups  of  the  animal 
kingdom,  but  finds  its  best  examples  among  the  coelenterates. 
Obelia  is  an  excellent  illustration  of  a  metagenetic  animal.  The 
asexual  generation,  the  colony  of  polyps  (Fig.  73,  A),  forrns  buds 
of  two  kinds,  the  hydra  11  ths  and  the  gonangia.  The  medusae 
(Fig.  73,  B),  or  sexual  generation,  reproduce  the  colony  J^y 
means  of  eggs  and  spermatozoa. 

The  polyp  and  mechisa  stages  are  not  equally  important  in  all 
Hydrozoa  ;  for  example.  Hydra  has  no  medusa  stage  and  Geryonia 
no  polyp  or  hydroid  stage.  Various  conditions  may  be  illustrated 
by  different  Hydrozoa.  In  the  following  list,  O  represents  the 
fertilized  ovum,  H,  a  polyp,  M  a  medusa,  m  an  inconspicuous  or 
degenerate  medusa,  and  h  an  inconspicuous  or  degenerate  polyp.  , 

1.  O  — H  — O  — H  — O(^y^m). 

2.  H  —  m  —  O  —  H  —  m  —  O  (Sertularia). 

3.  O  —  H  —  M  —  O  —  H  —  M  —  O  (Obelia). 

4.  O  —  h  —  M  —  O  —  h  —  M  —  O  (Liriope). 
5.0  —  M  —  O  —  M — O  (Geryonia). 

c.  A  Jellyfish  or  Medusa  —  Gonionemus 

The  structure  of  a  hydrozoan  jellyfish  or  medusa  may  be  illus- 
trated by  Gonionemus  (Fig.  74).  This  jellyfish  is  common  along 
the  eastern  coast  of  the  United  States.  It  measures  about  half 
an  inch  in  diameter,  without  including  the  fringe  of  tentacles 
around  the  margin.  In  general  form  it  is  similar  to  the  medusa 
Qi_Qbelia  (Fig.  73,  B).    The  convex  or.  aboral  surface  is  caUsi—.^ 


PHYLUM   COELENTERATA 


123 


the  exumhrella:  the  concave,  or  oral  surface,  the  subumbrella. 
The  subumbrella  is  partly  closed  by  a  perforated  membrane 
called  the  velum.  Water  is  taken  into  the  subumbrellar  cavity 
and  is  then  forced  out  through  the  central  opening  in  the  velum 
by  the  contraction  of  the  body;  this  propels  the  animal  in  the 
opposite  direction,  thus  enabling  K  to  swim  about. 

The  tentacles,  which  vary  in  number  from  sixteen  to  more  than 
eighty,  are  capable  of  considerable  contraction.  Near  their  t^s 
are  adhesive  or  suctorial 
J>ads  at  a  point  jyhere  the 
tentacle  bends  at  a  sharp 
angle.  Hanging  down  into 
the  subumbrellar  cavity  is 
the  manubrium  with  the 
mouth  at  the  end  sur- 
rounded by  four  frilled 
oral    lobes.      The    mouth 

•    .  ,  ,  Fig.  74.  —  Gonionemus,  a  hydrozoan  jelly- 

opens  mtO  a  ^(iLStroyascillar         fish.     (Prom  Washburn,  after  Hargitt.) 

cavity  which  consists  of  a 

central  '^  stomach  "  and  four  radial  canals.^   The  radial  canals  enter 

a  circumferential  canal  which  lies  near  the  margin  of  the  umbrella. 

The  cellular  layers  in  Gonionemus  are  similar  to  those  in  Hvdra. 
but  the  mesoslea  is  extremely  thick  and  gives  the  animal  a  jeUy- 
like  cons^^t^^nqy.  Scattered  about  beneath  the  ectoderm  are 
many  nerve  cells,  and  about  the  velum  is  a  nerve  ring.  Sensory 
cells  with  a  tactile  function  are  abundant  on  the  tentacles.  The 
margin  of  the  umbrella  is  supplied  with  two  kinds  of  sense  organs : 
(i)  at  the  base  of  the  tentacles  are  round  bodies  which  contain 
pigmented  entoderm  cells  and  communicate  with  the  circumfer- 
ential canal;  (2)  between  the  bases  of  the  tentacles  ^^  small  out- 
growths which  are  probably  organs  of  equilibrium  and,  therefore, 
statocysts.  Muscle  fibers,  both  exumbrella  and  subumbrella, 
are  present,  giving  the  animal  the  power  of  locomotion. 

Suspended  beneath  the  radial  canals  are  the  sinuously  folded 
reproductive   organs  or  gonads.     Gonionemus  is  dioecious,  each 


124 


COLLEGE  ZOOLOGY 


individual  prndiiringr  either  eggs  or  spermatozoa.  These  repro- 
ductive cells  break  out  directly  into  the 
water,  where  fertilization  takes  plare, 
A  ciliated  planula  develops  from  the 
egg  as  in  Ohelia  (Fig.  73,  C).  This 
soon  becomes  fixed  to  some  object,  and 
a  mouth  appears  at  the  unattached 
end.  Then  four  tentacles  grow  out 
around  the  mouth  and  the  Hydra-like 
larv^a  is  able  to  feed  (Fig.  75).  Other 
similar  Hydra-like  larvae  bud  from  its 


Fig.  75.  —  Hydralike  stage 

in  the  development  of  Gonio-  walls.     How  the  medusse  arise  from 

^r^'r^-^^^'^^'^rTT,^?  these  larvs  is  not  known,  but  it  seems 

IS   carrying    a   worm    (w)    to  ' 

the    mouth.     Tentacles   in  probable   that  a  direct   change   from 

crb-d;tt"u.arHilry:  'he    hydroid    form    to    th.    medusa 

after  Perkins.)  OCCUrS. 


d.  Hydroid  and  Medusa  Compared 

Although  the  medusae  upon  superficial  examination  appear  to 
be  very  different  from  the  polyps  or  hydroids,  they  are  con- 
eci- ^ 


r:-rad 


Fig.  76.  —  Diagrams  showing  the  similarities  of  a  polyp  (A)  and  a  medusa 
(B).  circ,  circular  canal;  ect,  ectoderm;  end,  entoderm;  ent.  cav,  gastrovascu- 
lar  cavity;  hyp,  hypostome;  mnb,  manubrium;  msgl,  mesoglea;  mth,  mouth; 
nv,  nerve  rings;  rad,  radial  canal;  v,  velum.     (From  Parker  and  Haswell.) 


PHYLUM   CCELENTERATA 


125 


structed  on  the  same  general  plan  as  the  latter.  Figure  76  illus- 
trates in  a  diagramatic  fashion  the  resemblance  between  the 
polyp  (A)  and  the  medusa  (B)  by  means  of  longitudinal  sections. 
If  the  medusa  were  grasped  at  the  center  of  the  aboral  surface 
and  elongated,  a  hydra-like  form  would  result.  Both  have  sim- 
ilar parts,  the  most  noticeable  _^^ifference..  b^.i^g,  the  .eaoniimis 
quantity  of  mesoglea  (fnsgl)  present  in  the  medusa. 


Fig.  77.  —  Physalia  or  Por- 
tuguese man-of-war,  a  colonial 
Hydrozoon.     (After  Agassiz.) 


Fig.  78.  —  Diagram  showing 
possible  modifications  of  medu- 
soids  and  hydroids  of  a  hydro- 
zoan  colony  of  the  order  Sipho- 
NOPHORA.  e,  gastrozooid  with 
branched,  grappling  tentacle,  /; 
g,  dactylozooid  with  attached 
tentacle,  h;  i,  generative  medu- 
soid;  k,  nectophores  (swimming 
bells);  /,  hydrophyllium  (cover- 
ing piece)  ;  m,  stem  or  corm; 
n,  pneumatophore.  The  thick 
black  line  represents  etjtgderm, 
the  thinner  line  ec^toderm.  (From 
Lankester's  Treatise,  after  All- 
man.) 


126 


COLLEGE  ZOOLOGY 


e.  Polymorphism 

The  division  of  labor  among  the  cells  of  a  Metazoon  has  al- 
ready been  noted  (p.  74).  When  division  of  labor  occurs  among 
the  members  of  a  colony,  the  form  of  the  individual  is  suited  to 
the  function  it  performs.  A  mlony  mntaining  two  kind^  nf 
members  is  said  to  be  dimorlyhin:  one  rnntainina  mnrp  fTi^n 


two 


kinds^  ^plymorphic.  Some  of  the  most  remarkable  cases  of 
polymorphism  occur  among  the  Hydrozoa.  The  "  Portuguese 
man-of-war  "  (Fig.  77),  for  example,  consists  of  a  float  with  a 
sail-like  crest  from  which  a  number  of  pol3^s  hang  down  into  the 
water.  Some  of  these  polyps  are  nutritive,  others  are  tactile; 
some  contain  batteries  of  nematocysts,  others  are  male  repro- 
ductive zooids,  and  still  others  give  rise  to  egg-producing  me- 
dusae. 

Tables  V  and  VI  present  briefly  the  various    modifications 
that  may  occur  among  the  members  of  colonial  Hydrozoa. 

TABLE   V 

POLYMORPHIC   MODIFICATIONS    OF   THE   MEDUSOIDS    OF  THE   HYDROZOA 


Name 

Structure 

Function 

Sexual  medusoid 

Like  typical  medusa  of  An- 

Production  of  ova  or 

thomedusae    (p.    128),   or 

spermatozoa 

modified   because   of   ar- 

rested development  (Fig. 

78,  i) 

Nectophore 

Without  tentacles,   manu- 
brium, and  mouth  (Fig. 
78,^) 

Locomotion 

Hydrophyllium 

Shield  shaped  (Fig.  78,  /) 

Protective 

Pneumatophore 

Air  sac  (Fig.  78,  n) 

Hydrostatic 

Aurophore 

Ovoid 

Unknown 

PHYLUM   CCELENTERATA 


127 


TABLE   VI 

POLYMORPHIC  MODIFICATIONS  OF  THE  HYDROIDS  OF  THE  HYDROZOA 


Name 

Structure 

Function 

Gastrozooid 

With  large  mouth,  nemato- 
cysts,  and  tentacle  bear- 
ing nematocysts  (Fig.  78, 

Ingestion  of  food 

Dactylozooid 

Without      mouth ;       with 
many    nematocysts    and 
tentacle  (Fig.  78,  g,  h) 

Offense  and  defense 

Blastostyle 

Without  mouth  or  tentacles 

Produces  sexual  me- 
dusoids  by  budding 

/.  Reproduction  in  the  Hydrozoa 

The  methods  of  reproduction  difYer  so  widely  among  the  Hy- 
B^ozoA  that  only  a  brief  general  account  can  be  given  here. 
Reference  should  be  made  to  the  descriptions  for  Hydra  (p.  115), 
Obelia  (p.  121),  and  Gonionemus  (p.  123). 

Asexual  reproduction  is  characteristic  of  some  Hydrozoa  and 
rare  or  absent  in  others.  The  most  common  method  is  by  bud- 
dim  {Hydra,  p.  1.15,  Fig.  65).  The  wall  of  the  hydroid  sends 
out  a  hollow  protrusion  w^hich  may  become  either  a  new  hydroid 
or  a  medusa.  Certain  medusae  also  produce  medusae  by  bud- 
ding. Fission  is  rare  in  hydroids  {Hydra,  p.  116,  Fig.  71)  and 
very  rare  in  medusae. 

Sexual  Reproduction.  —  Both  male  and  female  germ-cells  are 
rarelv  developed  bv  a  single  iiKli\-i(]u:il  as  in  Hydra  (Fig.  65). 
Usually  a  colony  produces  either  ova  or  spermatozoa,  or  these 
originate  in  different  indi\iduals  of  a  single  colony.  Sometimes 
one  blastostyle  may  give  rise  to  both  kinds  of  germ-cells.  The 
develoi)ment  of  the  fertilized  egg  has  already  been  described  in 
Hydra  (p.  116),  Obelia  (p.  121),  and  Gonionemus  (p.  124). 


128  COLLEGE  ZOOLOGY 

g.  Classification  of  the  Hydrozoa 

The  Hydrozoa  may  be  distinguished  from  the  Scyphozoa 
and  Anthozoa  by  the_  absence  of  a  stomodaeum  and  mesen- 
teries  (Fig.  84),  and  by  the  fact  that  their  sexual  ^cells  ar^  dis- 
charged directly  to  the  exterior.  In  classifying  the  Hydrozoa, 
both  the  hydroids  and  medusae  are  considered.  The  arrange- 
ment adopted  in  this  book  is  from  Fowler  in  Lankester's  Treatise 
on  Zoology. 

Order  i.  Anthomedusae.  Hydrozoa  usually  with  two 
forms  of  individuals,  (i)  non-sexual  fixed  hydroids,  and  (2)  fixed 
or  free-swimming  sexual  medusae.  The  perisarc  (absent  in 
Hydra)  does  not  form  hydrothecae  around  the  polyp  nor  gono- 
thecae  around  the  reproductive  zooids.  The  reproductive  or- 
gans are  in  the  wall  of  the  manubrium.  The  hydroids  are  usually 
colonial,  with  solid  tentacles  in  one  or  more  whorls.  Examples: 
Hydra,  Hydractinia,  Eudendrium,  Tubularia. 

Order  2.  Leptomedusae.  —  Hydrozoa  with  an  alternation 
of  non-sexual  fixed  hydroids  and  free  or  fixed  sexual  medusae. 
The  hydrothecae  and  gonothecae  are  specialized  portions  of 
the  perisarc.  The  sexual  organs  are  on  the  radial  canals.  The 
medusae  possess  eye-spots  (ocelli)  and  statocysts  containing 
statoliths  of  ectodermal  origin.  Examples:  Obelia  (Fig.  73), 
Campanularia,  Plumularia,  Sertularia,  Clytia. 

Order  3.  Trachjmiedusae. — Hydrozoa  without  alternation 
of  generatloi^s,  the  medusa  developing  more  or  less  directly  from 
the  eg;g.  The  sexual  organs  are  on  the  radial  canals.  The 
medusae  possess  sensory  organs  called  tentaculocysts,  contain- 
ing entodermal  statoliths  which  are  usually  enclosed  in  vesicles. 
Examples:    Trachynema,  Persa,  and  Liriope. 

Order  4.  Narcomedusae.  —  Hydrozoa  without  alternation 
of  generations.  The  sexual  organs  are  on  the  subumbral  floor 
of  the  gastric  cavity  or  gastric  pouches.  The  tentaculocysts 
contain  entodermal  statoliths  w^hich  are  not  enclosed  in  vesicles. 
Examples:    Cunocantha,  Cunina, 


PHYLUM    CCELENTERATA  1 29 

Order  5.  Hydrocorallinae.  —  Colonial  Hydrozoa  with  alter- 
nation of  generations  and  a  massive  Qr_^raii(;;)iing.jpjJC£tieflii5. 
skeleton  into  which  the  nutritive  polyps,-. (gastrozooids). and 
protective  polyps  (dactylozooids)  may  be  drawn.  These  Hydro- 
coralline  are  often  called  corals  and  are  found  on  coral  reefs, 
but  they  differ  in  structure  fromvthe  true  corals  (Figs.  86-91). 
Example:  Millepora.  The  stsighorn  com\  (Millepora  alcicornis) 
occurs  in  Florida. 

Order  6.  Siphonophora.  —  Colonial  free-swimming  Hydro- 
zoa with  alternation  of  generations  and  hii^^hly  modified  (poly- 
morphic)  hydroid  and  medusoid  members.  Example:  Physalia 
(Portuguese  man-of-war,  Fig.  77).  The  hydroids  and  medu- 
soids  of  the  Siphonophora  may  be  modified  as  shown  in  Tables 
V  and  VI. 

3.   Class  II.     Scyphozoa 

Most  of  the  larger  jellyfishes  belong  to  the  Scyphozoa. 
They  can  be  distinguished  easily  from  the  hydrozoan  medusae 
by  the  presence  of  notches,  usually  eight  in  number,  in  the  margin 
of  the  umbrella.  They  are  called  acraspedote  (without  velum 
or  craspedon)  medusa?  in  contrast  to  the  craspcdote  (with  velum 
or  craspedon)  m.edusa?  of  the  Hydrozoa.  The  Scyphozoa 
range  from  an  inch  to  three  or  four  feet  in  diameter.  They  are 
usually  found  floating  near  the  surface  of  the  sea,  though  some 
of  them  are  attached  to  rocks  and  weeds.  There  is  an  alterna- 
tion of  generations  in  their  life-history,  but  the  asexual  stage 
(th^  scyphistoma,  Fig.  81,  B)  is  subordinate. 

a.   A  Scyphozoan  Jellyfish  —  Aurelia 

Aurelia  (Fig.  79)  is  one  of  the  commonest  of  the  scyphozoan 
jellyfishes.  The  species  A.Jayidula_  ranges  from  the  coast  of 
Maine  to  Florida.  Members  of  the  genus  may  be  recognized 
by  the  eight  shallow  lobes  of  the  umbrella  margin,  and  the  fringe 
of  many  small  tentacles. 

In    structure    Aurelia    differs    from    Gonionemus   and   other 

K 


I30 


COLLEGE  ZOOLOGY 


hydrozoan  medusae  in  the  absence  of  a  velum,  the  characteristics 
of  the  canal  system,  the  position  of  the  gonads,  and  the  arrange- 
ment  and  morphology  of  the  sense-organs. 


Fig.  79.  —  Aurelia,  ventral  view  with  two  of  the  oral  arms  {or. a)  removed. 
a.r.c,  adradial  canal;  gon,  gonads;  i.r.c,  interradial  canal;  mg.lp,  marginal 
lappet;  mth,  mouth;  or.a,  oral  arm;  p.r.c,  perradial  canal;  s.g.p,  sub- 
genital  pit;    t,  tentacles.     (From  Parker  and  Haswell.) 


The  oral  lobes  or  lips  of  Aurelia  (Fig.  79,  or.a)  which  hang 
down  from  the  square  mouth  (mth)  are  long  and  narrow  with 
folded  margins.  The  mouth  opens  into  a  short  mllet,  which  leads 
to  the  somewhat  rectangular  "stomach.^'  A  gastric  pouch 
extends   laterally   from   each    side    of   the   stomach.      Within 


PHYLUM   CCELENTERATA 


131 


each  gastric  pouch  is  a  go7iad  (Fig.  79,  gon)  and  a  row  of 
small  gastric  filaments  bearing  nematocysts.  Numerous  r/idial 
canals  {Fig,  'jg,  a.r.c,i.r.c,  p.r.c),  some  of  which  branch  several 
times,  lead  from  the  stomach  to  a  circumferential  canal  at  the 
margin.  The  gonads  {gon)  are  frill-like  organs  lying  in. the  floor 
of  the  gastric  pouches.  They  have  a  pinkish  hue  in  the  living 
rr,ij  animal.     The    eggs    or    spermatozoa    pass 

through  the  stomach  and  out  of  the  mouth. 
The    eight    sense-ormns    of    Aurelia    lie 

between  the  marginal  lappets  (Fig.  79,  mg. 

Ip)  and  are  known  as  tentaculocvsts.     They 


Con  \  T 
Fig.  80.  —  Marginal 
sense-organ  (tentaculo- 
cyst)  of  Aurelia  in 
longitudinal  section. 
A,  superior  or  aboral 
olfactory  pit  ;  B,  in- 
ferior or  adoral  olfac- 
tory pit  ;  con,  ento- 
dermal  concretion 
(equilibrium);  End,  en- 
toderm; Ent,  entoder- 
mal  canal  continued 
into  the  tentaculocyst; 
H,  bridge  between  the 
two  marginal  lappets; 
oc,  ectodermal  pigment 
(ocellus);  T,  tentaculo- 
cyst. (From  Lankes- 
ter's  Treatise,  after 
Eimer.) 


Fig.  81.  —  Stages  in  development  of  Aurelia. 
A,  hydra-tuba  on  stolon  which  is  forming  new 
buds  at  I  and  2.  B,  later  stage,  or  strobila,  with 
strobilization  beginning.  C,  strobilization  more 
advanced.  D,  free-swimming  Ephyra  stage. 
E,  same  as  D  seen  in  profile.  (From  Shipley  and 
MacBride,  after  Sars.) 


are  considered  to  be  organs  of  equilibrium.  As  shown  in  Figure 
80,  each  tentaculocyst  ( T)  is  a  hollow  projection  connected  with 
the  entodermal  canal  {Ent).  It  contains  a  number  of  calcareous 
concretions  {Con)  formed  by  the  entoderm  {End);  and  bears  an 
ectodermal  pigment  spot,  the  ocellus  {oc),  which  is  sensitive  to 
light.  The  tentaculocyst  is  protected  by  an  aboral  hood  and  by 
lateral  lappets.     Olfactory  pits  {A  and  B)  are  situated  near  by. 


132  COLLEGE  ZOOLOGY 

An  alternation  of  generations  occurs  in  Aurelia,  but  the  hydroid 
stage  is  subordinate.  The  eggs  develop  into  free-swimming 
planulae  which  become  attached  to  some  object  and  produce 
hydra-like  structures,  each  of  which  is  called  a  hydra-tuba 
(Fig.  81,  A).  This  buds  like  Hydra  during  most  of  the  year, 
but  finally  a  peculiar  process  called  strobilization  takes  place. 
The  hydra-tuba  divides  into  discs  w^hich  cause  it  to  resemble 
a  pile  of  saucers  (B) ;  at  this  stage  it  is  known  as  a  strobila. 
Each  disc  develops  tentacles  (C),  and,  separating  from  those 
below  it,  swims  away  as  a  minute  medusa  called  an  ephyra 
(D,  E).     The  ephyra  gradually  develops  into  an  adult  jellyfish. 

b.   Classification  of  the  Scyphozoa 

Four  orders  of  Scyphozoa  are  usually  recognized.  The  most 
obvious  ordinal  characteristics  are  the  presence  or  absence  of 
stomodaeum  and  mesenteries,  and  the  position  of  the  tentacles 
and  tentaculocysts.  The  stomodceum  or  sullet  is  a  passageway 
between  the  mouth  and  the  gas tro vascular  cavity  or  "  stomach"; 
it  is  often  held  in  place  by  membranes  called  mesenteries.  The 
position  of  the  tentacles  and  tentaculocysts  is  described  with 
regard  to  their  relation  to  the  four  radial  canals.  Those  at  the 
ends  of  the  radial  canals  are  said  to  be  perradial  (Fig.  79,  p.r.c) ; 
those  halfway  between  two  perradii  are  called  interradial  (i.r.c) : 
and  those  halfway  between  a  perradius  and  an  interradius  are 
termed  adradial  (a.r.c) . 

Order  i.  Stauromedusae.  —  Scyphozoa  without  tentacu- 
locysts: tentacles  perradial  and  interradial;  umbrella  goblet- 
shaped:  sometimes  attached  by  the  aboral  pole;  a  stomodaeum 
is  present,  suspended  by  four  mesenteries;  no  alternation  of 
generations.     Examples:    Tessera  (Fig.  82,  A),  Lucernaria. 

Order  2.  Peromedusae.  —  Scyphozoa  with  four  interradial 
tentaculocysts-  tentacles  perradial_  and  adradial;  umbrella 
conical,  with  transverse  constriction;  a  stomodaeum  is  present 
suspended  by  four  mesenteries;  no  alternation  of  generations. 
Example:  Periphylla  (Fig.  82,  B). 


PHYLUM   CCELENTERATA 


133 


Order  3.     Cubomedusae.  —  Scyphozoa  with    four    perradial 
tentaculocysts;   tentacles  interradial;   umbrella  four-sided,  cup^ 


Fig.  82.  —  Scyphozoa.  A,  Tessera  prince ps,  order  St avromedvsm.  B,  Peri- 
phylla  hyacinthina,  order  Peromedus^.  C,  Charybdea  marsupialis,  order  Cubo- 
medusae. G,  gonads;  Gf,  gastral  filaments;  Ov,  gonads;  Rf,  annular  groove; 
Rk,  marginal  bodies;  Rm,  circular  muscle;  T,  tentacles.  (From  Sedgwick, 
after  Haeckel.) 

shaped;    no  alternation  of  generations.     Example:    Charybdea 
(Fig.  82,  C). 
Order  4.     Discomedusae.  —  Scyphozoa  with   four  or    more 

perradial  and  four  or  more  interradial  tentaculocysts ;   umbrella . 

_disc-shapedi alternation   of   generations.     Examples:    Aurelia 

(Fig.  79),  Pelagia,  Cassiopea. 


4.   Class  III.    Anthozoa  (Actinozoa) 

There  are  no  medusae  among  the  Anthozoa.  The  polyps 
may  be  distinguished  from  those  of  the  Hydrozoa  by  the  pres- 
ence of  a  well-developed  stomodaeum  or  gullet,  which  is  fastened 
to  the  body-wall  by  a  number  of  radially  arranged  membranes 
called  mesenteries.  Many  of  the  polyps  are  solitary,  but  the 
majority  produce  colonies  by  budding.     Most  of  the  Anthozoa 


134 


COLLEGE  ZOOLOGY 


secrete  a  calcareous  skeleton,  known  as  coral.  Two  types  are 
described  in  the  following  pages:  (i)  the  sea-anemone,  and 
(2)  the  coral  polyp. 

a.   A  Sea-Anemone  —  Metridium 

Metridium    marginatum   (Fig.    8.^)    is   a   sea-anemone   which 
fastens  itself  to  the  piles  of  wharves  and  to  solid  objects  in  tide- 
pools  along  the  North  Atlantic  coast.     It  is  a  cylindrical'  ani- 
mal with  a  crpwn  of  hollow  tentacles  arranged  in  a  number  of 
,.^  ^  circlets    about  '  the    slit,-like 

€Mw&^4h£&m'^^^  well  as  the  body  can,  be  ex- 
panded and  contracted,  and 
the  animal's  position  may  be 
changed  by  a  sort  of  creeping 
movement  of  its  lasal  disc. 
The  skin  is  soft  but  tough 
and  contains  no  skeletal  struc- 
tures. The  tentacles  capture 
small  organisms  by  means  of 
nemntnr.ysts^  and  carry  the 
food  thus  obtained  into  the 
mouth.  The  beating  of  the 
cU'a  which  cover  the  tentacles 


Fig.   83.  —  A  sea-anemone.     (From 
Weysse,  after  Emerton.) 


and  part  of  the  mouth  and  m^l  t  is  necessary  to  force  the  food 
into  the  gastr.o'jig^cular  cavity.  At  each  end  of  the  gullet,  or 
stomodceum  (Fig.  84,  4),  is  a  ciliated  groove  called  the  sipho- 
noglyphe  (Fig.  84,  j).  Usually  only  one  or  two  srphonoglyphes 
are  present,  but  sometimes  three  occur  in  a  single  specimen. 
A  continual  stream  of  water  is  carried  into  the  body  cavity 
through  these  siphonoglyphes,  thus  maintaining  a  constant 
supply  of  oxygenated  water. 

If  a  sea-anemone  is  dissected  as  shown  in  Figure  84,  the 
central  or  ^astrovascular  (cfplen'eric)  cavity  will  be  found  to 
consist  of  six  radial  chambers:   these  lie   between  the  gullet  or 


PHYLUM    CCELENTERATA 


135 


stomodaeum  and  the  body- wall,  and  open  into  a  common  basal 
cavity.  The  six  pairs  of  thin,  double  partitions  between  these 
chambers  are  called  primary  septa  or  mesenteries  (Fig.  84,  10; 


Fig.  84.  —  Metridium  marginatum,  a  sea-anemone,  partly  cut  away  so  as  to 
show  its  structure,  i,  intermediate  zone;  2,  lip;  j,  siphonoglyphe;  4,  gullet ; 
5,  inner  end  of  gullet;  6,  edge  of  mesentery;  7,  cavity  of  a  tentacle;  8,  inner 
ostium;  p,  outer  ostium;  10,  primary  mesentery;  11,  muscle-band  on  primary 
mesentery;  12,  abnormal  tertiary  mesentery;  13,  secondary  mesentery;  14, 
tertiary  mesentery;  15,  quaternary  mesentery;  16,  reproductive  gland;  17, 
mesenterial  filament;  18,  opening  for  mesenterial  filament.  (Redrawn  from 
Linville  and  Kelly.) 


Fig.  85,  p.m).  Water  passes  from  one  chamber  to  another 
through  pores  (ostia.  Fig.  84,  9,  <^)  in  these  mesenteries.  Smaller 
mesenteries  project  out  from  the  body-wall  into  the  chambers, 


136 


COLLEGE  ZOOLOGY 


but  do  not  reach  the  stomodaeum;  these  are  secondary  mesen- 
teries  (Fig.  84,  ij;  Fig.  85,  s.m).  Tertiary  mesenteries  (Fig. 
84,  14;  Fig.  85,  t.m)  and  quaternary  mesenteries  (Fig.  84,  15) 
lie  between  the  primaries  and  secondaries.  There  is  considerable 
variation  in  the  number,  position,  and  size  of  the  mesenteries 
(Fig.  84,  12). 

Each   mesentery   possesses   a    longitudinal    retractor   muscle 
hand  (Fig.  84,  11).     The  bands  of  the  pairs  of  mesenteries  face 
^  each  other  except  those  of  the  pri- 

maries opposite  the  siphonoglyphes. 
These  primaries,  which  are  called 
directives  (Fig.  85,  d),  have  the  muscle 
bands  on  their  outer  surfaces.  The 
edges  of  the  mesenteries  below  the 
stomodaeum  are  provided  w^ith  mesen- 
teric filaments  having  a  secretory  func- 
tion. Near  the  base  these  filaments 
bear  long,  delicate  threads  called 
acontia  (Fig.  84,  ly).  The  acontia 
are  armed  w^th  ^land  cells  and 
nematocysts,  and  can  be  protruded 
from  the  mouth  or  through  minute 
pores  (cinclides)  in  the  body-wall 
They  probably  serve  as  organs  of  offense  and 


Fig.  85.  —  Cross-section  of  a 
sea-anemone  showing  the  ar- 
rangement of  the  mesenteries. 
d,  directives ;  p.m,  primary 
mesentery  ;  s,  siphonoglyphe; 
s.m,  secondary  mesentery  ; 
t.m,  tertiary  mesentery.  (From 
Weysse.) 


(Fig.  84,  18). 
defense. 

Near  the  edge  of  the  mesenteries  lying  parallel  to  the  mesen- 
teric filaments  are  the  gonads  (Fig.  84,  16).  The  animals  are 
dioecious,  and  the  eggs  or  spermatozoa  are  shed  into  the  gastro- 
vascular  cavity  and  pass  out  through  the  mouth.  The  fertilized 
egg  probably  develops  as  in  other  sea-anemones,  forming  first 
a  free-swimming  planula  and  then,  after  attaching  itself  to  some 
object,  assuming  the  shape  and  structure  of  the  adult. 

Asexual  reproduction  is  of  common  occurrence,  new  anemones 
being  formed  by  budding  or  fragmentation  at  the  edge  of  the 
basal  disc.     Longitudinal  fission  has  also  been  reported. 


PHYLUM    CCELENTERATA 


137 


h.   A  Coral  Polyp  —  Astrangia 

Astrangia  dance  (Fig.  86)  is  a  coral  polyp  inhabiting  the  waters 
of  our  North  Atlantic  coast.     A  number  of  individuals  live  to- 


Fig.  86.  —  Astrangia  dance,  a  cluster  of  our  Northern  coral-polyps,  resting  on 
limy  bases  of  their  own  secretion.     (From  Davenport,  after  Sourel.) 

gether  in  colonies  attached  to  rocks  near  the  shore.     Each  polyp 

looks  like  a  small  sea-anemone,  being  cylindrical  in  shape  and 

possessing  a  crown  of  tentacles. 

The  most  noticeable  difference 

is  the  presence  of  a  basal  cup 

of   calcium   carbonate   termed 

the   theca   (Fig.   87   p).     This 

structure  of  calcium  carbonate 

is    what    we    commonly    call 

coral.     It  is  produced  by  the 

ectoderm   of   the   coral  polvp 

and  increases  gradually  during 

the  life  of  the  animal. 

The  calcareous  cui?  is  divided 
into  chambers  by  a  number  of 
mdial  sej)ta  (Fig.  87,  11)  which 
are  built  up  between  the  pairs 
of  mesenteries  {4)  of  the  polyp. 
The  center  of  the  cup  is  ocgi- 
pied  by  a  columdlaSio)  formed 


Fig.  87.  —  Semi-diagrammatic  view 
of  half  a  simple  coral,  i,  tentacle; 
2,  mouth  ;  3,  gullet ;  4,  mesentery  ; 
5,  edge  of  mesentery ;  6,  ectoderm ; 
7,  entoderm;  8,  basal  plate;  q,  theca; 
10,  columella ;  11,  septum.  (From 
Shipley  and  MacBride,  partly  after 
Bourne.) 


138  COLLEGE   ZOOLOGY 

in  part  by  the  fusion  of  the  inner  ends  of  septa,  and  in  part 
by  projections  from  the  base  of  the  polyp.  Although  Astrangia 
builds  a  cup  less  than  half  an  inch  in  height,  it  produces 
enormous  masses  of  coral  in  the  course  of  centuries. 

c.  Coral  Reefs  and  Atolls 

Coral  polyps  build  fringing  reefs,  harrier  reefs,  and  atolls. 
These  occur  where  conditions  are  favorable,  principally  in  tropi- 
cal seas,  the  best  known  being  among  the  Maldive  Islands  of 
the  Indian  Ocean,  the  Fiji  Islands  of  the  South  Pacific  Ocean, 


Fig.  88.  —  A  small  atoll,  being  ii  sketch  of  Whitsunday  Island  in  the 
South  Pacific.     (From  Sedgwick,  after  Darwin.) 

the  Great  Barrier  Reef  of  Australia,  and  in  the  Bahama  Island 
region. 

A  frin^in^  or  shore  reef  is  a  ridge  of  coral  built  up  from,  the 
sea  bottom  so  jiear  the  land  that  no  navigable  channel  exists 
between  it  and  the  shore.  Frequently  breaks  occur  in  the  reef, 
and  irregular  channels  and  pools  are  created  which  are  often 
inhabited  by  many  different  kinds  of  animals,  some  of  them 
brilliantly  colored. 

A  barrier  reef  is  separated  from  the  shore  by  a  wide,  deep 
channel.  The  Great  Barrier  Reef  of  Australia  is  over  iioo 
miles  long  and  encloses  a  channel  from  10-25  fathoms  deep  and 
in  some  places  30  miles  wide.  Often  a  barrier  reef  entirely 
surrounds  an  island. 


PHYLUM   CCELENTERATA  139 

An  atoll  (Fig.  88)  is  a  more  or  less  circular  reef  enclosing  a 
lagoon.  Several  theories  have  been  advanced  to  account  for  the 
production  of  atolls.  Charles  Darwin,  who  made  extensive 
studies  of  coral  reefs  and  islands,  is  responsible  for  the  subsidence 
theory.  According  to  Darwin,  the  reef  was  originally  built  up 
around  an  oceanic  island  which  sloi^vly  sank  beneath  the  ocean, 
leaving  the  coral  reef  enclosing  a  lagoon.  John  Murray  be- 
lieves that  the  island  enclosed  by  the  reef  does  not  necessarily 
sink,  but  may  be  worn  down  by  erosion. 

Besides  producing  islands  and  reefs,  corals  play  an  important 
role  in  protecting  the  shore  from  being  worn  down  by  the  waves. 
They  have  also  built  up  thick  strata  of  the  earth's  crust. 

d.   Classificatio7i  of  the  Anthozoa 

The  Anthozoa  may  be  divided  into  two  subclasses  and  ten 
orders. 

Subclass  I.  Alcyonaria.  —  Anthozoa  with  eight  hollow, 
pinnate  tentacles,  and  eight  complete  mesenteries;  with  one 
siphonoglyphe,  ventral  in  position;  and  with  the  retractor  muscles 
of  the  mesenteries  all  on  the  side  toward  the  siphonoglyphe. 

Order  i.  Stolonifera.  — Alcyonaria  colonial  in  habit;  with 
stolon  attached  to  a  stone  or  other  foreign  object;  polyps  free 
except  at  base  or  joined  together  by  horizontal  bars;  skeleton 
either  horny  or  of  calcareous  spicules.  Example:  Tuhipora 
(Fig.  89,  A). 

The  organ-pipe  coral,  Tuhipora  (Fig.  89,  A),  is  common  on 
coral  reefs.  It  has  bright  green  tentacles  and  a  skeleton  of  a  dull 
red  color,  and  adds  considerably  to  the  beauty  of  the  coral  reef. 

Order  2.  Alcyonacea.  —  Colonial  Alcyonaria;  zooids  united 
into  a  compact  mass  by  fusion  of  body-walls  ;  skeleton  of 
calcareous  spicules  which  do  not  form  a  solid  axial  support. 
Example:    Alcyonium  (Fig.  89,  B). 

Order  3.  Gorgonacea.  —  Colonial  Alcyonaria;  skeletal 
axis  branched  and  not  perforated  by  gastrovascular  cavities  of 
the  zooids.     Example:    Cor  allium  (Fig.  89,  C). 


146 


College  zoology 


This  order  includes  the  sea-fans  which  are  to  be  found  in 
almost  every  museum,  and  the  precious  red  coral  {Coralliuniy 
Fig.  89,  C),  which  occurs  in  the  Mediterranean  and  is  widely 
used  in  the  manufacture  of  jewelry. 

Order  4.  Pennatulacea.  —  Alcyonaria  forming  bilaterally 
symmetrical  colonies;    zooids  usually  borne  on  branches  of  an 


Fig.  89.  —  Coral.  A,  Tubipora  musica,  organ-pipe  coral,  a  young  colony. 
Hp,  connecting  horizontal  platforms;  p,  skeletal  tubes  of  the  zooids;  St^ 
the  basal  stolon.  B,  Alcyonium  digitatum,  with  some  zooids  expanded.  C, 
CoralUum,  a  branch  of  precious  coral.  P,  polyp.  D,  Pennatula  sulcata,  a  sea- 
feather.  (A  and  B,  from  Cambridge  Natural  History;  C,  from  Sedgwick,  after 
Lacaze  Duthiers;    D,  from  Sedgwick,  after  Kolliker.) 

axial  stem,  which  is  supported  by  a  calcareous  or  horny  skeleton. 
Examples:  Pennatula  (Fig.  89,  D),  Renilla.  The  sea-pens 
(Fig.  89,  D)  live  with  their  stalks  embedded  in  muddy  or  sandy 
sea-bottoms.     Many  of  them  are  phosphorescent. 


PHYLUM   CCELENTERATA 


141 


Subclass  II.  Zoantharia.  —  Anthozoa  with  usually  many 
simple  hollow  tentacles,  arranged  generally  in  multiples  of  five 
or  six;  two  siphonoglyphes  as  a  rule;  mesenteries  vary  in  num- 
ber, the  retractor  muscles  never  arranged  as  in  the  Alcyonaria; 
skeleton  absent  or  present;  simple  or  colonial;  dimorphism  rare. 

Order  i.  Edwardsiidea.  —  A  fejv  shallow  water  Zoantharia 
with  eight  complete  mesenteries  and  from  fourteen  to  twenty 
or  more  tentacles. 

Order  2.  Actiniaria.  —  Zoantharia  usually  solitary ;  many 
complete  mesenteries;  no  skeleton.  Examples:  Metridium 
(Fig.  84),  Halcampa,  Bunodes. 

These  are  the  sea-anemones.  Some  of  them  are  parasitic; 
Bicidium  is  parasitic  on  the  jellyfish  Cyanea.  Many  sea- 
anemones  are  beautifully  colored;  in  the  large  Stoichactis  of  the 
Great  Barrier  Reef  of  Australia,  "  the  spheroidal  bead-like 
tentacles  occur  in  irregularly  mixed  patches  of  gray,  white, 
lilac,  and  emerald  green,  the  disk  being  shaded  with  tints  of  gray, 
while  the  oral  orifice  is  bordered  with  bright  yellow."     (Kent.) 

Order  3.  Madreporaria.  —  Zoantharia  usually  colonial; 
many  complete   mesenteries;    calcareous   skeleton   formed   by 


Fig.  90.  —  Oculina 
speciosa,  a  branch  of 
madreporarian  coral. 
(From  Sedgwick, 
after  Ed.  H.) 


Fig.  91.  —  Meandrina,  a  rose-coral  of  the 
order  Madreporaria.     (From  Weysse.) 


142  COLLEGE   ZOOLOGY 

ectoderm  cells.  Examples:  Astrangia  (Fig.  86),  Oculina  (Fig. 
90),  and  Madrepora. 

Most  of  the  stony  corals  belong  to  this  order.  Astrangia 
has  already  been  described  (p.  137,  Fig.  86).  Oculina  (Fig.  90) 
and  Madrepora  are  branching  corals.  Meandrina  (Fig.  91)  is 
a  more  compact  ''  brain  "  coral.  Many  of  the  coral  polyps  are 
tinted  with  pink,  lilac,  yellow,  green,  violet,  red,  etc.,  and  give 
the  coral  reefs  the  wonderful  color  effects  for  which  they  are 
famous. 

Order  4.  Zoanthidea.  —  Zoantharia  usually  colonial ;  only 
one  siphonogl)^he;  mesenteries  differ  from  those  of  Actiniaria; 
no  skeleton,  but  often  incrusted  by  sand. 

Certain  Zoanthidea  are  the  black  corals  of  the  Mediterranean ; 
others  live  symbiotically  with  hermit  crabs  or  sponges. 

Order  5.  Antipathidea.  —  Colonial  Zoantharia  with  a  horny, 
usually  branching  axial  skeleton,  but  no  calcareous  spicules. 

The  corals  belonging*  to  this  order  are  found  in  all  the  large 
seas,  usually  at  a  depth  of  from  fifty  to  five  hundred  fathoms. 

Order  6.  Cerianthidea.  —  Solitary  Zoantharia  without 
a  skeleton;  one  siphonoglyphe;  no  bands  of  retractor  muscles  on 
mesenteries.     Example :    Cerianthus. 

This  order  contains  a  single  genus,  Cerianthus.  One  species 
C.  americanus,  occurs  on  the  eastern  coast  of  North  America; 
other  species  occur  in  widely  separated  localities. 

5.   Ccelenterates  in  General 

Definition.  —  Phylum  Cgelenterata.  —  Polyps,  Jelly- 
fishes,  Corals.  —  Diploblastic,  radially  symmetrical  animals, 
with  four  or  six  antimeres;  a  single  gastro vascular  cavity;  no 
anus;  body- wall  contains  peculiar  structures  known  as  nemato- 
cysts  or  stinging  cells. 

Morphology.  —  The  foregoing  account  has  shown  that  ccelen- 
terates all  possess  a  body-w^all  composed  of  two  layers  of  cells, 

an  i2]itSL-££k>dS£2^  e]'5.4...9L^jBS£L£Si2i^^™-  They  are  therefore 
diUoblastic.  although  many  Anthozoa   have  a  fairly  well  de- 


PHYLUM   CCELENTERATA  143 

veloped  mesoderm.  Between  these  layers  is  a  jelly-like  non- 
cellular  substance,  the  mesoglea.  The  body-wall  encloses  a 
single  cavity,  the  ccelenteron  or  mslrovasciUat:  cavity,  in  which 
both  diges.tiQn^g.niJ.,drr,ii]a,tion  ta-ke  placfi.  In  some  of  the  coe- 
lenterates,  like  Hydra  (Fig.  65),  this  cayity  is  simple,  but  in 
others,  like  Aurelia  (Fig.  79),  it  is  modified  so  as  to  include 
numerous  pouches  and  branchirfg   canals. 

The  two  principal  types  of  coelenterates  are  the  i)olvi?  or 
hydroid,  and  the  jellyfish  or  medusa.  These  are  fundamentally 
similar  in  structure  (Fig.  76),  but  are  variously  modified  (Tables 
V  and  VI).     Both  polyps  and  medusae  are  radially  symmetrical. 

So  far  as  is  known,  all  coelenterates  possess  stinging  cells 
called  nematncysts;  these  are  organs  of  offense  and  defense. 
MusrJp,  Jilfril.^  are  present  in  a  more  or  less  concentrated  con- 
dition. Nerve- fibers  and  sensory  organs  are  characteristic 
structures;  they  may  be  few  in  number  and  scattered  as  in 
Hydra  (p.  112),  or  numerous  and  concentrated  as  in  Aurelia 
(p.   131,   Fig.   80). 

Physiology.  —  The  food  of  coelenterates  consists  principally 
of  small,  free-swimming  animals,  which  are  usually  captured  by 
means  of  nem^tocysts  and  carried  into  the  mouth  by  tentacles 
and  cilia.  Digestion  is  mainly  extracellular,  enzymes  being  dis- 
charged into  the  gastroyascular  cavities  for  this  purpose. 
The  digested  food  is  transported  to  various  parts  of  the  body  by 
currents  in  the  gastrovascular  cavity,  and  is  then  taken  up  by 
the  entoderm  cells  and  passed  over  to  the  ectoderm  cells.  Both 
respiration  and  excretion  are  performed  by  the  general  surface 
of  the  ectoderm  and  entoderm.  Motion  is  made  possible  by 
muscle  fibrils,  and  many  species  have  also  the  power  of  loco- 
motion. There  is  no  true  skeleton,  although  the  stony  masses 
built  up  by  coral  polyps  support  the  soft  tissues  to  a  certain  ex- 
tent. The  nervous  tissue  and  sensory  organs  provide  for  the 
perception  of  various  kinds  of  stimuli  and  the  conduction  of  im- 
pulses from  one  part  of  the  body  to  another.  Coelenterates 
are  generally  sensitive  to  light  intensities,  to  changes  in  the 


144  COLLEGE  ZOOLOGY 

temperature,  to  mechanical  stimuli,  to  chemical  stimuli,  and  to 
gravity.  Reproduction  is  both  asexual,  by  budding  and  fission, 
and  sexual,  by  means  of  eggs  and  spermatozoa. 

Economic  Importance.  —  Coelenterates  as  a  whole  are  of  very 
little  economic  importance.  The  coral  built  up  by  coral  polyps 
form  reefs  and  islands  and  thick  strata  of  the  earth's  crust. 
Some  corals  are  used  as  ornaments  and  for  the  manufacture  of 
jewelry  (Fig.  89,  C).  Coelenterates  are  probably  very  seldom 
used  as  food  by  man  but  are  eagerly  devoured  by  fishes. 


CHAPTER  VI 


PHYLUM  CTENOPHORA 


The  Phylum  Ctenophora  (Gr.  ktenos,  of  a  comb;  phoreo, 
I  bear)  includes  a  small  group  of  free-swimming  marine  animals 
which  are  even  more  nearly  transparent  than  the  coelenterate 
jellyfishes.  They  have  been  pkced  by  many  authors  under 
the  Phylum  Ccelenterata,  but  the  present 
tendency  is  to  separate  them  from  that 
group  and  rank  them  as  a  distinct  phylum 
(p.  25).  They  are  widely  distributed,  being 
especially  abundant  in  warm  seas. 

Ctenophores  are  commonly  called  sea 
walnuts  heca^use  of  their  shape  (Fig.  92),  or 
comb  jellies  on  account  of  their  jelly-like 
consistency  and  the  comb-like  locomotor 
organs  arranged  in  eight  rows  on  the  sides 
of  the  body  (Fig.  93,  A,  5;  Fig.  93,  B,  dr). 
A  few  species  have  a  slender  ribbon-like 
shape  and  may,  like  Venus'  girdle  (Fig.  94), 
reach  a  length  of  from  six  inches  to  four 
feet. 

The  general  structure  of  a  ctenophore  is 
shown  in  Figure  93.  It  is  said  to  possess 
hiradial  symmetry,  since  the  parts,  though  in  general  radially 
disposed,  lie  half  on  one  side  and  half  on  the  other  side  of  a 
median  longitudinal  plane.  An  end  view,  as  in  Figure  93,  B, 
illustrates  this  fact.  The  mouth  (Fig.  93,  A,  i)  is  situated  at 
one  end  {oral)  and  a  sense-organ  fFig.  93,  A,  2)  at  the  opposite 
or  ahoral  end.  Extending  from  near  the  oral  surface  to  near 
L  14s 


Fig.  92.  — A  cteno- 
phore, Idyia  roseola. 
(From  Weysse,  after 
Agassiz.)  a,  excretory- 
pore  ;  b,  paragastric 
canal ;  c,  circular 
canal  ;  d-h,  ciliated 
bands.  (From  Weysse, 
after  Agassiz.) 


146 


COLLEGE  ZOOLOGY 


the  aboral  end  are  eight  meridional  ciliated  hands  (Fig.  93,  A,  5; 
Fig.  93,  B,  ctr)\  these  are  the  locomotor  organs.  Each  band  has 
the  cilia  arranged  upon  it  in  transverse  rows  and  fused  at  the 
base;  each  row  thus  resembles  a  comb.  These  are  raised  and 
lowered  alternately,  starting  at  the  aboral  end,  and  cause  an 
appearance  like  a  series  of  waves  travel- 
ing from  this  point  toward  the  mouth. 
The  animal  is  propelled  through  the 
water  with  the  oral  end  forward.  Light 
is  refracted  from  these  moving  rows  of 
cilia,  and  brilliant,  changing  colors  are 
thus  produced. 
Some  species  are 
phosphorescent. 
Most  cteno- 
phores     possess 


Fig.  93. 

Side  view. 
3,  funnel ; 


twosolid,  contrac- 
tile tentacles  (Fig. 
93,  A,  8)  which 
emerge  from  blind 
,-pouches  (Fig.  93, 
A,  7),  one  oh 
either  side  (Fig. 
.93,  B).  With  one 
exception,  the  ten- 
tacles are  not  pl^o- 
vided  with  nema- 
tocysts  as  are 
those  of  the 
CcELENTERATA,  but  are  supplied  with  adhesive  or  slue  cells  called 
colkMusM.  (Fig.  95).  The  coUoblasts  produce  a  secretion  of  use 
in  capturing  small  animals  which  serve  as  food.  The  spiral 
filament  {sf)  in  each  colloblast  is  contractile,  and  acts  as  a 
spring,  often  preventing  the  struggling  prey  from  tearing  the 
cell  away. 


A  B 

—  Ctenophora.     a,  Hormiphora  plurnosa. 

I,  mouth  ;  2,  aboral  pole  with  sense  organ; 

4,  paragastric  canal ;  5,  a  ciliated  band  ; 
6,  canal;  7,  tentacular  pouch;  8,  tentacle;  g,  gelatin- 
ous substance.  B,  Pleurobrachia  -pileus,  view  of  aboral 
aspect,  showing  central  statocyst,  polar  fields  (P/), 
and  eight  ciliated  bands  (ess,  c.tr).  (A,  from  Shipley 
and  MacBride,  after  Chun ;  B,  from  Lankester's 
Treatise.) 


PHYLUM   CTENOPHORA 


147 


The  Digestive  System. — The  mouth  (Fig.  93,  A,  i)  opens 
into  a  flattened  stomodcPMm.  where  most  of  the  food  is  digested; 


:/..  —  Cestus  veneris,  Venus'  girdle,     m,  mouth;  c^-(^,  ciliated  bands; 
st,  sfi,  x^,  x^,  canals.     (From  Lankester's  Treatise.) 

this  leads  to  the  "  infundibulum  "  or  funnel  (Fig.  93,  A,  j)  which 

is  flattened  at  right  angles  to  the  stomodaeum.     Six  canals  arise 

from  the  infundibulum.     Two  of  these,  called  excretory  canals. 

open  to  the  exterior  near  an  aboral  sense-organ; 

undigested  food  probably  does  not  pass  through 

them,  but  is  ejected  through  the  mouth.     The 

two  paramstric  canals  (Fig.  93,  A,  4)  lie  parallel 

to  the  stomodaeum,  ending  blindly  near  the 

mouth.     The  two   tentacular  canals  pass  out 

toward  the  pouches  of  the  tentacles,  then  each 

gives  rise  to  four  branches  (Fig.  93,  A,  6)  ; 

th^se  lead   into  meridional  canals  Ivirig  just 

beneath  the  ciliated  bands  (Fig.  93,  A,  5). 

The  aboral  sense-organ  (Fig.,tj6)  is  ^ J^Mocy.^L^cS^^\'^^^UmJt 
or  organ  of  equilibrium.  It  consists  of  a  vesicle  gl,  glandular  por- 
of  fused  cilia  {cu)  enclosing  a  ball  of  calcareous   ^J.^^^'  .^.^j  ^^^^^"y 

granules,  the  statolith  {ot),  which  is  supported    (From  Lankester's 

by  four  tufts  of   fused  cilia.     It  is  probable   Treatise,  after 
that  when  the  body  is  at  an  angle,  the  cal- 
careous ball  presses  more  heavily  on  the  inclined  side,  and  thus 
stimulates  the  ciliated  bands  on  that  side  to  greater  activity. 


Fig.  95.  —  Two 
adhesive  cells  from 
ctenophore.     cf. 


148  COLLEGE  ZOOLOGY 

Just  beneath  the  statocyst  is  a  ciliated  area  supposed  to  be 
sensory  in  function,  and  on  either  side  is  a  ciliated  prolongation 
called  the  polar  field  (Fig.  93,  B,  Pf). 

Ctenophores  are  hermaphroditic.  The  ova  are  formed  on  one 
side  and  the  spermatozoa  on  the  other  side  of  each  meridional 
canal  just  beneath  the  ciliated  bands 
(Fig.  93,  A,  5).  The  germ-cells  pass  into 
the  infundibulum  and  thence  to  the  out- 
side through  the  mouth.  The  fertilized 
eggs  develop  directly  into  the  adult 
without  the  intervention  of  an  asexual 
generation  as  in  many  coelenterates. 
Fig.  96.  —  Sense  organ  The  cellular  layers  of  ctenophores  con- 
tZZ^t'^rZ^:.  stitute  a  very  small  part  of  the  hs^, 
cu,  cupule  fornied  of  fused  most  of  it  being  composed  of  the  trans- 
(r^o^Linttei'sTrat  Parent  JeUy-like  M...^/ea.  The  thin 
ise.)  ciliated'  ectoderm  covers  the  exterior  and 

lines  the  stomodaeimi;  and  the  entoderm^ 
also  ciliated,  lines  the  infundibulum  and  the  canals  to  which 
it  gives  rise.  The  muscle  fibers  which  lie  just  beneath  the 
ectoderm  and  entoderm  are  derived  from  th.t  mesoderm  cells  of 
the  embryo.  Ctenophores  are  therefore  triploblastic  animals, 
and  represent  a  higher  grade  of  development  than  that  of  the 
coelenterates. 

Defini^on.  —  Phylum  Ctenophora.  —  Sea  Walnuts  or 
Comb  Jellies.  —  Triploblastic  animals;  radial  combined  with 
bilateral  symmetry  ;  eight  radially  arranged  rows  of  paddle" 
plates. 

The  Ctenophora  differ  from  the  coelenterates  in  several 
important  respects  besides  the  presence  of  a  distinct  mesoderm. 
With  one  probable  exception,  ctenophores  do  not  possess 
nematocysts,  and  the  adhesive  cells  (Fig.  95)  which  take  their 
place  are  not  homologous  to  nematocysts.  Their  ciliated  bands, 
aboral  sense-organs,  and  pronounced  biradial  symmetry  are 
peculiarities  which  warrant  placing  ctenophores  in  a  phylum, 


PHYLUM   CTENOPHORA  149 

by  themselves.  They  probably  evolved  from  coelenterate-like 
ancestors,  but  can  no  longer  be  combined  with  that  phylum. 
A  discussion  of  the  resemblances  between  ctenophores  and  the 
flatworms  (Platyhelminthes)  is  reserved  for  the  next  chapter 
(p.  166). 


CHAPTER  VII 
PHYLUM   PLATYHELMINTHES 

The  Phylum  Platyhelminthes  (Gr.  platus,  broad;  helmins, 
an  intestinal  worm)  includes  the  planarians,  liver-flukes,  tape- 
worms, and  many  other  "  flatworms."  Some  of  these  are  free 
living  in  fresh  water,  salt  water,  or  less  frequently  on  land, 
whereas  others  are  parasitic.  Many  of  the  parasites  pass  through 
a  number  of  complex  stages,  and  live  in  the  bodies  of  several 
species  of  animals  during  their  life-history.  The  parasitic  flat- 
worms  frequently  are  responsible  for  serious  diseases  of  man 
and  other  animals. 

The  three  classes  of  the  Platyhelminthes  are  as  follows :  — 

Class  I.  Tiirbellaria  (Lat.  turbo,  I  disturb),  with  ciliated 
ectoderm;    free-living  habit  { Planar ia,  Fig.  97); 

Class  II.  Trematoda  (Gr.  trema,  a  pore;  eidos,  resemblance), 
with  non-ciliated  ectoderm;  suckers;  parasitic  habit  {Fasciola, 
Fig.   105);    and 

Class  III.  Cestoda  (Gr.  kestos,  a  girdle;  eidos,  resemblance), 
with  body  of  segments;  without  mouth  or  ahmentary  canal; 
parasitic  {Tcenia,  Fig.  107). 

I.  A  Fresh- WATER  Flatworm  —  Planaria 

Planaria  (Fig.  97,  and  Fig.  98,  2)  is  a  flatworm  found  only 
ii]Lfi£sh^w^ter,jisjULally„cl«agii^ 

Jia  -body  .is  ]M.QL^Z^Uy-..syninietrical  and  dor§o-ventrally  flattened. 
The  anterior  end  is  rather  blunt,  the  posterior  end,  more  pointed. 
It  mav  reach  half  an  inch  in  length,^  Planaria  maculata,  the 
common  American  species,  is  difficult  to  study  because  of  the 

150 


PHYLUM   PLATYHELMINTHES 


151 


great  amount  of  coloring  matter  in  its  body  (Fig.  98,  2),  but  an 
allied  flatworm,  Dendroccelum  lacteum  (Fig.  98,   i),  is  cream- 
colored,  and  its  anatomy  is  more  easily  made  out. 
3  5 


Fig.  97.  —  Planaria  polychroa,  a  fresh-water  flatworm.  /,  eye;  2,  side  of 
head;  3,  proboscis;  4,  pharynx  sheath;  5,  genital  pore.  (From  Shipley  and 
MacBride.) 

Anatomy  and  Physiology.  —  External  Features.  —  Figure 
97  shows  the  principal  external  features  of  a  planarian.  A  pair 
of  eye-spots  (i)  are  present  on  the 
dorsal  surface  near  the  anterior  end. 
The  mouth  is  in  a  peculiar  position 
near  the  middle  of  the  ventral  sur- 
face. From  it  the  muscular  pro-  - 
boscis  (j)  may  extend.  Posterior 
to  the  mouth  is  a  smaller  opening, 
the  genital  pore  (^).  The  surface 
of  the  body  is  covered  with  ,ciUa 
which  propel  the  animni  thron^]i 
the,  water  This  is  not  the  only 
method  of  locomotion,  since  mus- 

riilnr  rnntrarfmn  ic;  akn  pffprtivp 

Internal  Anatomy  and  Physi- 
ology.—  A  study  of  the  structure 
of  the  adult  and  of  the  early  em- 
bryonic stages  shows  Planaria  to 
be  a  triplohlastic  animal  possessing 
three  germ-layers,  ectjod.ctVh^.JMS^ 
derm^  and  entoderm^  ^irom  which 
several  systems  of  organs  have  been 


Fig.  q8.  — '  Two  species  of 
fresh  water  flatworms.  i,  Den- 
droccelum  lacteum;  2,  Planaria 
maculata.  (From  Davenport, 
after  Woodworth.) 


2. 


152 


COLLEGE  ZOOLOGY. 


derived.  There  are  well-developed  muscular,  nervous,  digestive, 
excretory,  and  reproductive  systems;  these  are  constructed  in 
such  a  way  as  to  function  without  the  coordination  of  a  circu- 
latory system,  respiratory  system,  coelom,  and  anus. 

Digestive  System.  —  The 
digestive  system  (Fig.  99)  con- 
sists of  a  mouth  (m),  a  pharynx 
(ph)  lying  in  a  muscular  sheath, 
and  an  intestine  of  three  main 
trunks  (i,  ii,  is)  and  a  large 
number  of  small  lateral  exten- 
sions. The  muscular  pharynx 
can  be  extended  as  a  proboscis 
(Fig.  97,  j);  this  facilitates 
the  capture  of  food.  Digestion 
is  both  intercellular  and  intra- 
cellular, i.e.  part  of  the  food  is 
digested  in  the  intestinal  trunks 
by  secretions  from  cells  in  their 
walls;  whereas  other  food  par- 
ticles are  engulfed  by  pseudo- 
podia  thrust  out  by  cells  lining 
the  intestine,  and  are  digested 
inside  of  the  cells  in  vacuoles. 
The  digested  food  is  absorbed 
by  the  walls  of  the  intestinal 
trunks,  and,  since  branches 
from  these  penetrate  all  parts 
of  the  body,  no  circulatory 
system  is  necessary  to  carry, 
nutriment  from  one  place  to 
another.  As  in  Hydra,  no 
anus  is  present,  the  faeces 
being  ejected  through  the 
mouth. 


Fig.  99,  —  Anatomy  of  a  flatworm. 
en,  brain  ;  e,  eye  ;  g,  ovary  ;  i\,  i^,  is, 
branches  of  intestine;  In,  lateral  nerve; 
m,  mouth  ;  od,  oviduct ;  ph,  pharynx  ; 
/,  testis ;  u,  uterus ;  v,  yolk  glands; 
vd,  vas  deferens;  $ ,  penis;  $  ,  vagina; 
$  $ ,  common  genital  pore.  (From 
Lankester's  Treatise,  after  v.  GrafiF.) 


PHYLUM   PLATYHELMINTHES 


153 


Excretory  System.  —  The  excretory  system  comprises 
a  pair  of  longitudinaL  much-coiled_tubeSj^  one  on  each  side  of  the 
body;  these  are  connected  near  the  anterior  end  by  a  transverse 
tube,  and  open  to  the  exterior  by  two  small  pores  on  the  dorsal 
surface.  The  longitudinal  and  transverse 
trunks  give  off  numerous  finer  tubes  which 
ramifv  through  all  parts  of  the  bodv, 
usually  ending  in  a  flame-cell.  The  Hame- 
_  cell  fFig.  100)  is  large  and  hollow,  with  a 
bunch  of  flickering  ciha  {c)  extending  into 
the  central  cavity  {e).  Since  it  communi- 
cates only  with  the  excretory  tubules,  it  is 
considered  excretorv  in  function,  though  it 
m^y  also  carry  on  respiratory  activities. 

Muscular  System.  —  The  power  of 
changing  the  shape  of  its  body,  which  may 
be  observed  when  Planaria  moves  from 
place  to  place,  lies  principally  in  three  sets 
of  muscles:  a  circular  layer  just  beneath  Lankester's  Treatise.) 
the  ectoderm,  external  and  internal  layers 
of  longitudinal  muscle  fibers,  and  a  set  of  oblique  fibers  lying 
in  the  mesoderm. 

Nervous  System.  —  Planaria  possesses  a  well-developed 
nerv^ous  system  consisting^- of  _  a  bilobed  mass,  of. ._ti_ssue, just  be- 
neath the  eye-spots  called  the  brain  (Fig.  99,  en),  and  two  lat- 
eral longitudinal  nerve-cords  {In)  connected  by  transverse  nerves. 
From  the  brain,  nerves  pass  to  various  parts  of  the  anterior 
end  of  the  body,  imparting  to  this  region  a  highly  sensitive 
nature. 

Reproductive  System.  —  Reproduction  is  by  J^sion^or  by 
the  sexual  method.  Each  individual  possesses  both  male  and 
female  organs,  i.e.  is  hermaphroditic.  The  male  organs  may  be 
located  easily  in  Figure  99;  they  consist  of  numerous  spherical 
testes  (/)  connected  by  small  tubes  called  vasa  deferentia  (vd); 
the  vas  deferens  from  each  side  of  the  body  joins  the  cirrus  or 


Fig.  100. — Flame-cell 
of  Planaria.  c,  cilia ; 
e,  opening  into  excre- 
tory     tubule.       (From 


154 


COLLEGE   ZOOLOGY 


penis  ( ^  ),  a  muscular  organ  which  enters  the  genital  cloaca.  A 
seminal  vesicle  lies  at  the  base  of  the  penis,  also  a  number  of  uni- 
cellular, prostate  glands.  Spermatozoa  originate  in  the  testes, 
and  pass,  by  way  of  the  vasa  deferentia,  into  the  seminal  vesicle, 
where  they  remain  until  needed  for  fertilization. 


Fig.  ioi.  —  Development  of  Planaria  laclea.  i,  egg  (o)  surrounded  by 
yolk  (v).  2,  four  blastomeres  (W)  from  segmented  egg.  3,  later  stage;  blas- 
tomeres  (W)  more  numerous.  4,  much  later  stage;  blastomeres  differentiated 
into  ectoderm  (ep),  entoderm  (hy),  a  provisional  pharynx  (ph),  and  wandering 
cells  (w).  5,  cellular  differentiation  more  advanced;  ep,  ectoderm;  ent, 
primitive  gut;  hy,  entoderm;  ph,  pharynx.  6,  embryo  changes  shape  to  a 
flattened  ovoid;  eni,  primitive  gut;  m,  mouth;  ph,  pharynx.  (From  Lan- 
kester's  Treatise,  after  Hallez.) 

The  female  reproductive  organs  comprise  two  ovaries  (g),  two 
long  oviducts  (od)  with  many  yolk-glands  (v)  entering  them, 
a  vagina  (  $  )  which  opens  into  the  genital  cloaca,  and  the  uterus 
which  is  also  connected  with  this  cavity.  The  eggs  originate  in 
the  ovary,  pass  down  the  oviduct,  collecting  yolk  from  the  yolk- 
glands  on  the  way,  and  finally  reach  the  uterus,     Ji^re  fertiliza- 


PHYLUM  PLATYHELMINTHES 


155 


o 


/i<7W  occurs,  and  cocoons  are  formed,  each  containing  from  four 
to  more  than  twenty  eggs,  surrounded  by  several  hundred  yolk 
cells.  The  development  of  the  egg  is  illustrated  and  explained 
in  Figure  10 1. 

Regeneration.  —  Planarians  show  remarkable  powers  of  re- 
g^gneration.  If  an  individual  is  cu^in  two  (Fig.  102,  A),  the  an- 
terior end  wall  re- 
generate a  new  tail 
(B,  W),  while  the 
posterior  part  de- 
velops a  new  head 
(C,  CO.  A  cross- 
piece  (D)  will  re- 
generate both  a 
head  at  the  anterior 
end,  and  a  new  tail 
at  the  posterior  end 
(D'-D').  The  head 
alone  of  a  planarian 
will  grow  into  an 
entire  animal  {E- 
EP) .  Pieces  cut 
from  various  parts 
of  the  body  will 
also  regenerate 
completely.     No 

difficulty  is  experienced  in  grafting  pieces  from  one  animal 
upon  another,  and  many  curious  monsters  have  been  produced 
in  this  way. 


^, 


[I 


Fig.  102.  —  Regeneration  of  Planaria  macidata. 
A,  normal  worm.  B,  B^  regeneration  of  anterior 
half.  C,  CS  regeneration  of  posterior  half.  D,  cross- 
piece  of  worm.     D^,  D^,  D^,  D^,  regeneration  of  same. 

E,  old    head.      E^,  E^,  E',    regeneration    of    same. 

F,  F\  regeneration  of-  new  head  on  posterior  end  of 
old  head.     (From  Morgan.) 


2,   Class  I.    Tuebellaria 


The  TuRBELLARiA  (the  class  to  which  Planaria  belongs)  are 
free-living  Platyhelminthes  with  ciliated  epidermis.  Special 
ectodermal  cells  secrete  mucus  or  produce  rod-like  bodies  called 
''  rhabdites." 


156 


COLLEGE  ZOOLOGY 


Order  i.  Rhabdocoelida  (Fig.  103).  Small  Turbellarta, 
often  microscopic,  with  simple  unbranched  intestine.  Examples: 
Microstoma,  in  fresh  water;   Monoscelis  and  Monops,  marine. 

Order  2.  Tricladida  (Fig.  99).  Turbellaria  with  intestine 
of  three  main  branches — one  median  anterior  branch  {j})  and  two 


Fig.  10,5.  Plan  of  structure 
of  a  Rhabdococlous  Turbellarian. 
be,  bursa  copulatrix ;  en,  brain  ; 
«.  eye;  g,  germarium;  i,  intestine; 
In,  ventral  nerve  cord ;  m,  mouth ; 
ph.  pharynx;  rs,  seminal  recep- 
tacle ;  s,  salivary  gland ;  t,  testis  ; 
u,  uterus  containing  an  egg ; 
V,  shell  gland;  vs,  seminal  vesicle; 
$  ,  penis  ;  ^  $  ,  genital  pore. 
(From  Lankester's  Treatise,  after 
v.  Graff.) 


Fig.  104.  —  Plan  of  structure 
of  a  Polyclad  Turbellarian. 
D,  branches  of  intestine; 
G,  brain;  M.Go^,  male  genital 
pore  ;  O,  mouth  ;  Od,  oviduct ; 
Ov,  ova;  T,  vas  deferens;  V,  va- 
gina; W.Go^,  female  genital 
pore.  (From  Sedgwick,  after 
Quatrefages  ) 


lateral  posterior  branches  (i^,  i^) ;  many  lateral  caeca  arise  from 
the  main  branches.  Examples:  Planaria  (Fig.  98),  Polyscelis, 
and  Dendrocoelum  (Fig.  98,  i)  in  fresh  water;  Bipalium  in  the 
tropics  living  in  moist  earth,  and  accidentally  introduced  into 
hothouses  all  over  the  world;  Bdelloura,  Gunda,  and  Foly- 
chosrus  in  the  sea. 


PHYLUM   PLATYHELMINTHES  1 57 

Orders.  Poly cladida  (Fig.  104).  Marine Turbellaria  with 
a  central  digestive  chamber  which  gives  off  many  lateral  branches 
(D).     Examples:  Stylochus  and  Leptoplana. 

3.  Class  II.    Trematoda 

a.  The  Liver-fluke  —  Fasciola  hepatica 

The  liver-fluke  is  a  flatworm  which  lives  as  an  adult  in  the 
bile  ducts  of  the  liver  of  sheep,  cows,  pigs,  etc.,  and  is  occasionally 
found  in  man.  Figure  105  shows  the  shape  and  most  of  the  ana- 
tomical features  of  a  mature  worm.  The  mouth  (O)  is  situated 
at  the  anterior  end  and  lies  in  the  middle  of  a  muscular  disc, 
the  anterior  sucker.  A  short  distance  back  of  the  mouth  is  the 
ventral  sucker  (S) ;  it  serves  as  an  organ  of  attachment.  Between 
the  mouth  and  the  ventral  sucker  is  the  genital  opening  through 
which  the  eggs  pass  to  the  exterior.  The  excretory  pore  lies  at 
the  extreme  posterior  end  of  the  body,  and  another  pore,  the 
opening  of  Laurer's  canal,  is  situated  in  the  mid-dorsal  line 
about  one  third  the  length  of  the  body  from  the  anterior  end. 

The  digestive  system  is  simple.  The  mouth  (Fig.  105,  O)  opens 
into  a  short  globular  pharynx  which  leads  into  another  short 
tube,  the  oesophagus.  The  intestine  consists  of  two  branches, 
one  extending  from  near  the  anterior  to  the  posterior  end  on 
each  side  of  the  body.  Many  small  branches  (Fig.  105,  D)  are 
given  off  from  the  intestine  as  in  Planaria  (Fig.  99,  i),  and  no 
circulatory  system  is  therefore  necessary  for  the  transportation 
of  food  material. 

The  excretory  system  is  similar  to  that  of  Planaria  (p.  153),  but 
only  one  main  tube  and  one  exterior  opening  are  present.  The 
nervous  system  also  resembles  that  of  Planaria  (Fig.  99,  en,  In). 

The  suckers  are  provided  with  special  sets  of  muscles  enabling 
them  to  fasten  the  animal  to  its  host.  Three  layers  of  muscles 
lie  just  beneath  the  ectoderm:  (i)  an  outer  circular  layer,  (2)  a 
middle  longitudinal  layer,  and  (3)  an  inner  diagonal  layer. 

The  body  of  the  liver-fluke  is  triploblastic.     The  ectoderm  is  a 


158 


COLLEGE  ZOOLOGY 


thin,  hard  covering  often  called  the  cuticle;  it  protects  the  under- 
lying tissues  from  the  juices  of  the  host.     The  ectoderm  contains 

chitinous  scales  and  unicellular 
glands.  The  entoderm  lines  the 
alimentary  tract.  The  mesoderm 
is  represented  by  the  muscles, 
the  excretory  organs,  the  repro- 
ductive ducts,  and  the  paren- 
chyma. The  parenchyma  is  a 
loose  tissue  lying  between  the 
body-wall  and  the  alimentary 
canal;  within  it  are  embedded 
the  various  internal  organs  de- 
scribed above,  as  well  as  the 
reproductive  system. 

Both  male  and  female  reproduc- 
tive organs  are  present  in  every 
adult ;  they  are  extremely  well 
developed,  and,  as  in  Planaria^ 
quite  complex.  Those  of  the 
male  are  as  follows:  (i)  a  pair  of 
branched  testes  (Fig.  105,  T)  in 
which  the  spermatozoa  arise ; 
(2)  two  ducts,  the  vasa  deferentia, 
which  carry  the  spermatozoa  from 
the  testes  to  (3)  a  pear-shaped 
sac,  the  seminal  vesicle;  (4)  a  con- 
voluted tube,  the  ejaculatory  duct, 
which  leads  to  the  end  of  (5)  a 
muscular  copulatory  organ,  the 
penis. 

The  female  organs  are  (i)  a 
single-branched  ovary  (Fig.  105,  Dr)  in  which  the  eggs  are 
produced;  (2)  a  convoluted  oviduct  (Fig.  105,  Ov)  which  trans- 
ports the  eggs  from  the  ovary  to  (3)  the  shell  gland,  at  which 


Fig.  105.  —  The  liver  fluke,  Fas- 
ciola  hepatica.  D,  anterior  part  of 
intestine  (posterior  part  not  shown) ; 
Do,  yolk-glands;  Dr,  ovary; 
O,  mouth;  Ov,  uterus;  S,  sucker; 
T,  testes.  (From  Sedgwick,  after 
Sommer.) 


PHYLUM   PLATYHELMINTHES 


159 


place  (4)  the  vitelline  duct  brings  in  and  surrounds  the  eggs  with 
yolk  globules  derived  from  (5)  the  vitelline  glands  (Fig.  105,  Do)\ 
the  shell  gland  then  furnishes  a  chitinous  shell,  and  the  eggs  pass 
on  into  (6)  a  tube  called  the  uterus,  which  leads  to  the  genital  pore. 
One  liver-fluke  may  produce  as  many  as  five  hundred  thou- 
sand eggs,  and,  since  the  liver  of  a  single  sheep  may  contain  more 


\y 


Fig.  106.  —  Stages  in  the  life-history  of  the  liver  fluke,  Fasciola  hepatica. 
a,  miracidium  (ciliated  embryo),  b,  sporocyst  containing  rediae  (i?).  c,  a 
redia;  C,  cercaria;  D,  gut;  K,  germ-cells;  R,  redia.  d,  cercaria.  (From 
Sedgwick;   b,  after  Leuckart;    c  and  d,  after  Thomas.) 

than  two  hundred  adult -flukes,  there  may  be  one  hundred  million 
eggs  formed  in  one  animal.  The  eggs  segment  in  the  uterus  of  the 
fluke,  then  pass  through  the  bile  ducts  of  the  sheep  into  its  in- 
testine, and  finally  are  carried  out  of  the  sheep's  body  with  the 
faeces.  Those  eggs  that  encounter  water  and  are  kept  at  a  tem- 
perature of  about  75°  F.  continue  to  develop,  producing  a  ciliated 
larva  (Fig.  106,  a)  which  escapes  through  one  end  of  the  egg-shell 
and  swims  about.     This  larva,  called  a  miracidium,  possesses  a 


l6o  COLLEGE   ZOOLOGY 

double  eye-spot  on  the  dorsal  surface  near  the  anterior  end,  a 
pair  of  excretory  organs,  the  nephridia,  and  a  number  of  centrally 
placed  germ-cells.  It  swims  about  until  it  encounters  a  certain 
fresh-water  snail,  Lymncea  truncatula  of  Europe,  or  probably 
Lymncea  humilis  in  this  country.  If  no  snail  is  found  within 
eight  hours,  the  larva  dies. 

When  a  snail  is  reached,  the  larva  forces  its  anterior  papilla 
(Fig.  io6,  a)  into  its  tissue,  and  by  a  whirling  motion  bores  its  way 
into  the  soft  parts  of  the  body.  Here  in  about  two  weeks  it 
changes  into  a  sac-like  sporocyst  (Fig.  io6,  b).  Each  germ-cell 
within  the  sporocyst,  after  passing  through  blastula  and  gastrula 
stages,  develops  into  a  second  kind  of  larva,  called  a  redia  (Fig. 
io6,  b  R;  c).  The  rediae  soon  break  through  the  wall  of  the 
sporocyst  and  enter  the  tissue  of  the  snail.  Here,  by  means  of 
germ-cells  (Fig.  io6,  c,  K)  within  their  bodies,  they  usually  give 
rise  to  one  or  more  generations  of  daughter  redice  (Fig.  io6,  c,  7?), 
after  which  they  produce  a  third  kind  of  larva  known  as  a  cer- 
caria  (Fig.  io6,  c,  C).  The  cercariae  (Fig.  io6,  d)  leave  the  body 
of  the  snail,  swim  about  in  the  water  for  a  time,  and  then  encyst 
on  a  leaf  or  blade  of  grass.  If  the  leaf  or  grass  is  eaten  by  a 
sheep,  the  cercariae  escape  from  their  cyst  wall  and  make  their 
way  from  the  sheep's  alimentary  canal  to  the  bile  ducts,  where 
they  develop  into  mature  flukes  in  about  six  weeks. 

It  will  be  seen  from  the  above  description  that  the  life-history 
of  the  liver-fluke  is  complicated  by  the  interpolation  of  several 
generations  which  develop  from  unfertilized  germ-ceUs; 

(i)  The  fertilized  egg  produces  a  ciliated  larva,  the  miracidium 
(Fig.  io6,  a); 

(2)  The  miracidium  changes  to  a  sporocyst  ^yithin  which 
rediae  are  developed  from  unfertilized  germ-cells  (Fig.   106,  b); 

(3)  The  rediae  produce  other  rediae  from  unfertilized  germ- 
ceUs  (Fig.  106,  c); 

(4)  The  rediae  finally  give  rise  to  cercariae  from  unfertilized 
germ-cells  (Fig.  106,  d);  and 

(5)  The  cercariae  develop  into  mature  flukes  (Fig.  105). 


PHYLUM  PLATYHELMINTHES  l6l 

The  great  number  of  eggs  produced  by  a  single  fluke  is  neces- 
sary, because  the  majority  of  the  larvae  do  not  find  the  particular 
kind  of  snail,  and  the  cercariae  to  which  the  successful  larvae 
give  rise  have  little  chance  of  being  devoured  by  a  sheep.  The 
generations  within  the  snail  of  course  increase  the  number  of 
larva?  which  may  develop  from  a  .jingle  egg.  This  complicated 
life-history  should  also  be  looked  upon  as  enabling  the  fluke  to 
gain  access  to  new  hosts.  The  liver-fluke  is  not  so  prevalent 
in  the  sheep  of  this  country  as  in  those  of  Europe. 

h.    Trematoda  in  General 

The  Trematoda  are  parasitic  Platyhelminthes  without  cilia 
but  with  a  hardened  ectoderm  in  the  adult  stage.  The  body  is 
usually  flattened  and  leaf-shaped.  One  or  more  ventral  suckers 
are  present  at  or  near  the  posterior  end  and  in  the  mouth  region. 

Trematodes  may  be  ecto parasitic,  i.e.  living  on  the  body  of 
another  animal,  like  Gyrodactylus  which  clings  to  the  gills  of  the 
carp,  or  ento parasitic,  i.e.  living  in  the  body  of  another  animal, 
like  the  liver-fluke.  Some  of  the  modifications  due  to  parasitic 
habits  are  the  absence  of  eye-spots  in  most  species,  the  poorly 
developed  brain  and  sense-organs,  and  the  highly  specialized 
sexual  organs. 

The  two  orders  of  Trematoda  differ  principally  in  their  method 
of  development. 

Order  i.  Monogenea.  Trematodes  which  develop  directly 
from  the  egg;  they  possess  a  large  posterior,  ventral,  terminal 
sucker,  and  usually  one  or  two  suckers  near  the  mouth. 

Most  of  the  Monogenea  are  ectoparasitic  on  aquatic  animals, 
e.g.  Sphyranura  on  the  skin  of  the  salamander  (Necturus), 
Polystomum  on  the  gills  of  the  tadpole  and  later  in  the  urinary 
bladder  of  the  adult  frog,  and  Epihdella  on  the  body  of  the 
halibut. 

Order  2.  Digenea.  Entoparasitic  Trematoda  which  pass 
through  several  different  forms  in  their  life-history;  they  pos- 
sess an  anterior  and  often  a  ventral  sucker. 

M 


l62 


COLLEGE   ZOOLOGY 


The  best-known  member  of  this  order  is  the  liver-fluke,  which 
has  a  fairly  representative  life-history.  Usually  the  Digenea 
occupy  two,  but  sometimes  three,  hosts  during  their  development; 
one  host  is  generally  a  vertebrate,  one  a  snail,  and  the  third  an 
insect  or  other  animal.  Clonorchis  sinensis  and  Paragonimus 
ringeri  attack  human  beings  in  China.  A  few  Trematoda  and 
their  hosts  are  given  in  Table  VII.  (From  the  Cambridge 
Natural  History.) 

TABLE  VII 

THE   LIFE-raSTORIES   OF  A  FEW  DIGENETIC  TREMATODES 


Species 

Final  Host 

Host  Larva  enters 

AND  Cercari^ 

Formed 

Host  CERCARiiE 

enter ;     EATEN 

BY  Final  Host 

I.  Distomum 
atriventre 

Frogs  and  toads 
of       North 
America 

Physa      hetero- 
strophia,  a  snail 

Not  known. 

2.  D.  retusum 

The  frog,  Rana 

The  snail,  Lym- 
n(Ba  stagnalis 

The  snail,  Lym- 
ncBa  stagnalis, 
and  larvae  of 
caddice  flies. 

3.  Gasterosto- 
mum  fim- 
briatum 

Perch  and  pike, 
Perca        and 
Esox 

Fresh    water 

clams,     Unio 
and  Anodonta 

Leuciscus  ery- 
throphthalmus, 
a  small  fish. 

4.  Monosto- 
mum 
flavum 

Anas,  a  duck 

A  snail,  Planor- 
his  corneus 

Omitted. 

5.  Diplodiscus 
subclava- 
tus 

Frogs,  toads,  and 
salamanders, 
Rana,     Bufo, 
and  Triton 

Sna,i\.s,  Planorbis 
and  Cyclas 

Insect  larvae, 
frogs  {Rana) 
and  Toads 
{Bufo).  Often 
omitted. 

PHYLUM   PLATYHELMINTHES 


163 


4.   Class  III.    Cestoda 


a.  The  Tapeworm  —  Tcenia 

The  tapeworm,  Tcenia  solium,  is  a  common  parasite  which 
lives  as  an  adult  in  the  alimentary  canal  of  man.  A  nearly- 
related  species,  T.  saginata,  is  al^o  a  parasite  of  man.  Tcenia, 
as  shown  in  Figure  107,  is  a  long 
fiatworm  consisting  of  a  knob-like 
head,  the  ^c<^kx  (Fig.  107,  B),  and  a 
great  number  of  similar  parts,  the 
proglottides,  arranged  in  a  linear 
series.  The  animal  clings  to  the 
wall  of  the  alimentary  canal  by 
means  of  hooks  (Fig.  107,  B,  2)  and 
suckers  (j)  on  the  scolex.  Behind 
the  scolex  is  a  short  neck  {4)  follow^ed 
by  a  string  of  proglottides  which 
gradually  increase  in  size  from  the 
anterior  to  the  posterior  end.  The 
worm  may  reach  a  length  of  ten  feet 
and  contain  eight  or  nine  hundred 
proglottides.  Since  the 
proglottides  are  budded 
off  from  the  neck  (Fig. 
107,  B,  4),  those  at  the 
posterior  end  are  the 
oldest.  The  production 
of  proglottides  may  be 
compared  to  the  forma- 
tion of  ephyrae  by  the 
hydra- tuba  of  Aurelia 
(Fig.  81),  and  is  called 
strobilization. 

The    anatomy   of    the 
tapeworm  is  adapted  to 


Fig.  107.  —  The  tapeworm.  A,  Tcenia 
saginata.  The  approximate  lengths  of  the 
portions  omitted  in  the  drawing  are  giveii. 
At  *  the  branched  uterus  and  longitudinal 
and  transverse  excretory  vessels  are  shown. 
B,  head  or  scolex  of  Tcenia  solium,  i,  rostellum; 
2,  hooks;  5,  suckers;  4,  neck;  5,  commence- 
ment of  strobilization.  (A,  from  the  Cam- 
bridge Natural  History;  B,  from  Shipley  and 
MacBride.) 


164 


COLLEGE  ZOOLOGY 


ne.ru.  I- 


can..excreh  can  excret  J^g    parasitic 

habits.  There 
is  no  alimentary 
canal,  the  di- 
gested food  of 
the  host  be- 
ing absorbed 
through  the 
body-wall.  The 
gi.i/it  scAid      ^^    *'"'  nervous  system  is 

Fig.  108. — A  proglottis  of  the  tapeworm,  r«nja  5o^iMw,  Similar    to    that 

with  mature    reproductive  apparatus,     can.excret,  longi-  q£  Pldfidyld  and 
tudinal    excretory    canals    with    transverse    connecting 

vessels ;    gl.vit,    vitelline    or    yolk-glands ;    nerv.l,    longi-  the     iiver-lluke, 

tudinal  nerves;    ov,  ov,  ovaries;    por.gen,    genital   pore;  Kiif   r\Qf   cq  wpll 
schld,  shell-glands;   uter,  uterus;  vag,  vagina;  vas.def,  vas  j    /    • 

deferens.     The   numerous,  small,  round    bodies    are    the  developed    (rig. 

lobes  of  the  testes.     (From   Parker  and   Haswell,  after  jqQ        fierv       I) 
Leuckart.)  '   .         .  '         ^' 

Longitudinal  ex- 
r.rp.tnry  tubes,  with  branches  ending  in  flame-cells,  open  at  the 
posterior  end  and  carry  waste  matter  out  of  the  body  (Fig.  108, 
can.  excret.). 

A  mature  prodottid  is  almost  completely  filled  with  rei)roduc- 
tive  nr^an^s :  these 
are  shown  in 
Figure  108.  Sper- 
matozoa originate 
in  the  spherical 
testes,  which  are 
scattered  about 
through  the  pro- 
glottis; they  are 
collected  by  fine 
tubes  and  carried 
to  the  genital  pore 
{por.gen.)  by  way 
of  the  vas  deferens 


109.  —  Stages  in  the  development  of  the  tape- 
worm, Tcznia  solium,  to  the  cysticercus  stage,  a,  egg 
with  embryo,  b,  free  embryo,  c,  rudiment  of  the- 
head  as  a  hollow  papilla  on  wall  of  vesicle,  d,  bladder- 
worm  (cysticercus)  with  retracted  head,  e,  the  same 
with  protruded  head.  (From  Sedgwick,  partly  after 
Leuckart.) 


PHYLUM   PLATYHELMINTHES 


165 


^'*'SG 


(vas.def.).  Eggs  arise  in  the  bilobed  ovary  (ov)  and  pass  into 
a  tube,  the  oviduct  Yolk  from  the  yolk-gland  {gl.vit)  enters 
the  oviduct  and  surrounds  the  eggs.  A  chitinous  shell  is  then 
provided  by  the  shell  dand  (schld)  and  the  eggs  pass  into  the 
uterus  (uter).  The  eggs  have  in  the  meantime  been  fertilized 
by  spermatozoa,  which  probably  cdme  from  the  same  proglottis, 
and  move  down  the  vagina  (vag).  As  the  proglottides  grow 
older  the  uterus  becomes  distended  with  eggs  and  sends  off 
branches  (Fig.  107,*),  while  the  rest  of  the  reproductive  organs 
are  absorbed.  The  ripe  proglottides  break  off  and  pass  out  of 
the  host  with  the  faeces. 

The  eggs  of  Tcenia  solium  develop  into  six-hooked  embryos 
(Fig.  109,  a)  while  still  within  the  pro- 
glottis. If  they  are  then  eaten  by  a  pig, 
they  escape  from  their  envelopes  (Fig. 
109,  b)  and  bore  their  way  through  the 
walls  of  the  alimentary  canal  into  the 
voluntary  muscles,  where  they  form  cysts 
(Fig.  109,  c).  A  head  is  developed  from 
the  cyst  wall  (Fig.  109,  d)  and  then 
becomes  everted  (e).  The  larva  is  known 
as  a  MQ^d^lr^HL^'f^  -Qr.  .Qy^lK^^(^.^s  ^t  this 
stage.  If  insufficiently  cooked  pork  con- 
taining cysticerci  is  eaten  by  man,  the 
bladder  is  thrown  off,  the  head  becomes 
fastened  to  the  wall  of  the  intestine,  and 
a  series  of  proglottides  is  developed. 


M... 


h.   Cestoda  in  General 

The  Cestoda  are  all  entoparasitic  fiat- 
worms,  called  tapeworms ;  they  inhabit 
the  alimentary  canal  of  vertebrates  in  the 
adult  stage.  The  body  consists  of  a  head 
or  "  scolex  "  followed  by  a  chain  of  similar 
joints  or  "  proglottides  "  which  are  budded 


Fig.  1 10.  —  A  uniseg- 
mental cestod,  Archigetes 
sieboldii,  from  the  coelom 
of  a  worm,  Tubifex 
rivulorum.  app,  persist- 
ent larval  appendage; 
go,  genital  pore;  hk,  per- 
sistent larval  hooks ; 
ov,  ovary ;  sc,  sucker ; 
te,  testes ;  yg,  yolk- 
glands.  (From  the 
Cambridge  Natural  His- 
tory, after  Leuckart.) 


i66 


COLLEGE  ZOOLOGY 


off  from  the  "neck."  Archigetes  (Fig.  no)  differs  from  other 
tapeworms  both  in  structure  and  habit;  it  has  only  one  proglot- 
tis, and  lives  in  the  coelom  of  an  annelid,  Tubifex. 

A  few  Cestodes  and  their  hosts  are  given  in  Table  VIII  (from 
the  Cambridge  Natural  History). 

TABLE  VIII 

THE   LIFE-HISTORIES   OF   A   FEW   CESTODES 


Name 

Final  Host 

Intermediate  Host 

I. 

Taenia  saginata 

Man 

Ox,  giraffe  (in  muscles). 

2. 

T.  serrata 

Dog 

Rabbit,  hare,  mice  (liver  and 
peritoneum) . 

3- 

Dipylidium  cani- 
num 

Man,  dog,  cat 

Flea  of  dog  (body-cavity). 

4- 

Hymenolepis  di- 

Man,  mouse,  rat 

Meal-moth,  Asopia  farinalis; 

minuta 

also  certain  Orthoptera  and 
Coleoptera. 

5- 

Drepanido  taenia 

Goose 

Water-flea,  Cyclops  hrevicau- 

setigera 

datus. 

6. 

Bothriocephalus 
latus 

Man,  dog 

Pike,  perch,  trout,  etc. 

5.   Flatworms  in  General 

Definition.  —  Phylum  Platyhelminthes.  —  Flatworms.  — 
Triploblastic  animals;  bilaterally  symmetrical;  single  gastro- 
vascular  cavity;  no  anus;  presence  of  coelom  doubtful. 

The  flatworms  are  more  highly  organized  than  the  Cgelen- 
TERATA  or  Ctenophora  and  are  distinctly  triUoblastic.  The 
middle  germ-layer,  the  mesoderm,  which  is  well  developed  in  flat- 
worms,  is  connected  with  several  important  systems  of  organs, 
since  it  is  from  this  layer  that  the  muscles,  the  excretory  system, 
and  the  reproductive  ducts  originate.     The  development  of  these 


PHYLUM   PLATYHELMINTHES  167 

systems  of  organs  is  correlated  with  the  thickness  of  the  body- 
wall.  The  excretory  system  is  necessary,  since  it  is  no  longer 
possible  for  the  animal  to  get  rid  of  the  waste  products  of  metabo- 
lism through  the  general  surface  of  the  body.  Likewise  a  system 
of  ducts  is  required  to  transport  the  germ-cells  to  the  exterior. 
No  circulatory  system  appears  in  the  flatworms,  but  in  most  cases 
the  food  is  transported  directly  to  'the  tissues  through  the  much- 
branched  digestiye  tract,  which  seryes,  as  in  the  Ccelenterata 
and  Ctenophoila.,  as  a  gastroyascular  cayity. 

Definite  bilateral  symmetry  is  exhibited  by  flatworms  and 
should  be  considered  an  adyance  in  morphological  deyelopment, 
since  the  most  successful  animals  haye  their  bodies  constructed 
on  this  plan.  With  bilateral  symmetry  is  probably  correlated 
the  concentration  of  neryous  tissue,  the  brain,  in  the  head;  the 
end  of  the  body  directed  forward  in  moying  would  receiye  sen- 
sations first,  and  nerye-cells  would  be  dey eloped  in  the  region  of 
greatest  stimulation.  It  is  belieyed  by  some  authorities  that 
'the  body-cayity  in  the  laryal  stages  (sporocyst  and  redia)  of 
liyer- flukes  represents  the  coelom  (p.  89)  and  that  the  reproduc- 
tiye  ducts  of  the  adults  should  be  considered  true  ccelomic 
cayities.  , 

Our  present  knowledge  of  the  flatworms  seends  to  indicate  that 
they,  as  well  as  the  Ctenophora,  haye  eyolyed  from  ccelenterate 
stock.  Forms  like  the  simplest  Turbellaria,  the  Rhadocce- 
LiDA,  haye  probably  giyen  rise  to  the  more  complex  members 
of  that  class.  From  these  also  were  probably  deriyed  the 
Trematoda,  no  doubt  in  response  to  the  changed  conditions  of 
life  resulting  from  a  parasitic  habit.  Many  of  the  adult  Ces- 
TODA  appear  so  closely  related  to  certain  Trematoda  that  these 
two  classes  may  haye  arisen  together,  or  else  the  former  haye 
become  separated  from  the  complex  Trematoda  (Digenea)  as 
a  distinct  group.        ' 

Some  authorities  belieye  that  the  two  curious  animals  Cteno- 
plana  and  Coeloplana  are  connecting  links  between  the  Cteno- 
phora and  Platyhelminthes.     Ctenoplana  has  been  recorded 


I 68  COLLEGE  ZOOLOGY 

once  from  the  Indian  Ocean  and  once  from  New  Britain.  Coslo- 
plana  inhabits  the  Red  Sea. 

Economic  Importance  of  Flatworms.  —  The  Turbellaria  are 
of  practically  no  economic  importance.  Trematodes  are  para- 
sitic in  a  great  many  vertebrates,  but  for  the  most  part  do  not 
cause  serious  injuries.  The  liver-fluke  of  the  sheep,  and  the 
trematode  Schistosoma  hcBmatobium  which  infests  the  blood- 
vessels of  the  urinary  bladder  and  alimentary  tract  of  man,  in 
Africa,  are  the  most  important  species. 

The  adult  tapeworms  found  in  the  alimentary  canal  of  man 
and  other  animals  interfere  seriously  with  the  digestion  and 
absorption  of  food,  but  the  larvae  are  more  dangerous.  For 
example,  the  tapeworm,  Tcenia  echinococcus,  which  lives  as  an 
adult  in  the  dog,  gives  rise  to  a  larva  called  Echinococcus  poly- 
morphus.  These  larvae  may  form  large  vesicles  in  man,  known 
to  physicians  as  hydatides,  which  may  break  with  serious  or  even 
fatal  results.  The  organism  which  causes  "  gid  "  or  "  staggers  " 
in  sheep  is  the  larva,  called  Coenurus  cerebralis,  of  the  dog  tape- 
worm, Tcenia  cosnurus.  It  becomes  lodged  in  the  brain  or 
spinal  cord.  Goats,  cattle,  and  deer  are  also  attacked  by  the 
same  species.  'imiv'  '  MilihM  ^/ 


CHAPTER  vVIII 

PHYLUM    NEMATHELMINTHES 

The  Nemathelminthes  (Gr.  nema,  thread;  helmins,  an  in- 
testinal worm)  are  called  roiind  or  thread  worms.  They  are 
usually  long  and  slender,  and  more  or  less  cylindrical.  They 
may  be  distinguished  from  the  segmented  worms  (Phylum  An- 
nelida, Chap.  XI)  by  the  entire  absence  of  internal  and  external^ 
segmentation.  The  microscopic  animal  which  lives  in  vinegar 
and  is  known  as  the  vinegar-eel  is  a  nemathelminth.  Other 
roundworms  live  as  parasites  in  the  alimentary  canal  of  man, 
and  other  animals,  or,  like  Trichinella  (Fig.  113),  live  for  a  time 
embedded  in  the  tissues  of  the  body. 

I.  A  Parasitic  Roundworm  —  Ascaris  lumbricoides 

External  Features.  —  Ascaris  (Fig.  iii)  is  a  genus  of  round- 
worms parasitic  in  the  intestines  of  pigs,  horses,  and  man.  The 
sexes  are  separate.  The  female,  being  the  larger,  measures  from 
five  to  eleven  inches  in  length  and  about  one  fourth  of  an  inch 
in  diameter.  The  body  is  light  brown  in  color;  it  has  a  dorsal 
and  a  ventral  white  narrow  stripe  running  its  entire  length,  and 
a  broader  lateral  line  is  present  on  either  side.  The  anterior  end 
possesses  a  mouth  opening,  surrounded  by  one  dorsal  and  two 
ventral  lips  (Fig.  112  a,  ^,  c).  Near  the  posterior  end  is  the  anal 
opening  from  which,  in  the  male,  extend  penial  setce  (Fig.  112  a, 
a,  Sp.)  for  use  during  copulation.  The  male  can  be  distin- 
guished from  the  female  by  the  presence  of  a  bend  in  the  pos- 
terior part  of  the  body  (Fig.  112  a,  a). 

169 


lyo 


COLLEGE  ZOOLOGY 


Internal      Anatomy.  —  If     an 

animal  is  cut  open  along  the 
dorsal  line  (Fig.  iii),  it  will  be 
found  to  contain  a  straight  ali- 
mentary canal^  and  certain  other 
organs,  lying  in  a  central  cavity, 
the  coelom.  The  alimentary  canal 
(2)  is  very  simple,  since  the  food 
is  taken  from  material  already 
digested  by  the  host  whose  in- 
testine the  worm  inhabits.  It 
opens  at  the  posterior  end  through 
the  anus,  which  is  not^  present 
in  t^he  members  of  the  phyla 
already  discussed.  A  muscular 
pharynx  (/)  draws  the  fluids 
into  the  long  non-muscular  in- 
testine (2),  through  the  walls  of 
which  the  nutriment  is  absorbed. 
Just  before  the  anal  opening  is 
reached,  the  intestine  gradually 
becomes  smaller;  this  portion  is 
knowTi  as  the  rectum. 

The  excretory  system  consists  of 
two  lonsitudinal  canals  (Fig.  111,7) 
one  in  each  lateral  line;  these  open 
to  the  outside  by  a  single  pore  (<^) 
situated  near  the  anterior  end 
in  the  ventral  body-wall  (Fig. 
112  a,  c,P). 

A  ring  of  nervous  tissue  surrounds 
the  pharynx  and  gives  off  two  large 
nerve-cords,  one  dorsal,  the  other 
ventral,  and  a  number  of  other 
smaller  strands  and  connections. 


PHYLUM  NEMATHELMINTHES 


171 


The  male  reproductive  ormns  are  a  single,  coiled  thread-like 
testis,  from  which  a  vas  deferens  leads  to  a  wider  tube,  the  seminal 
vesicle;  this  is  followed  by  the  short  muscular  ejaculatory  duct 
which  opens  into  the  rectum.  In  the  female  lies  a  Y-shaped 
reproductive  system.  Each  branch  of  the  Y  consists  of  a  coiled 
thread-like  ovary  (Fig.  in,  j)  whi^h  is  continuous  with  a  larger 
canal,  the  uterus  (4),  The  uteri  of  the  two  branches  unite  into 
a  short  muscular  tube,  the  vagina  (5),  which  opens  to  the  outside 
through  the  genital  aperture  (6).  Fertilization  takes  place  in 
the  uterus.     The  egg  is  then  surrounded  by  a  shell  of  ckitin,  and 


Fig.  112  a.  —  Parts  of  Ascaris  liimbricoides.  a,  hind  end  of  male  with  the 
two  penial  setae  {Sp).  b,  anterior  end  from  the  dorsal  side,  showing  the  dorsal 
lip  with  its  two  papillae,  c,  the  same  from  the  ventral  side  with  the  two  lateral 
ventral  Ups  and  the  excretory  pore  (P).  d,  egg  with  external  membrane  of 
small  clear  spherules.     (From  Sedgwick,  after  Leuckart.) 


passes  out  through  the  genital  pore.  The  chitinous  egg-shell 
prevents  the  digestion  of  the  egg  within  the  intestine  of  the  host. 

The  relations  of  the  various  organs  to  one  another,  as  well 
as  the  structure  of  the  body- wall,  and  the  character  of  thec^om, 
are  shown  in  Figure  112b,  which  is  a  transverse  section  ofafemale 
specimen  of  Ascaris  lumbricoides.  The  body  of  the  worm  should 
be  considered  as  consisting  of  two  tubes,  one  the  intestine  (int.), 
lying  within  the  other,  the  body-wall;  while  between  them  is  a 
cavity,  the  coelom,  in  which  lie  the  reproductive  organs  {ovy. 
and  ut). 

The  body-wall  is  composed  of  several  layers,  an  outer  chitinous 
cuticle  (cu),  a  thin  layer  of  ectoderm  (der.epthm)  just  beneath  it, 


172 


COLLEGE  ZOOLOGY 


and  a  thick  stratum  of  longitudinal  muscle  fibers  (m),  mesodermal 
in  origin,  lining  the  coelom.  Thickenings  of  the  ectoderm  form 
the  dorsal  (d.l),  ventral  (v.v),  and  lateral  (lat.l)  lines.  In  each 
of  the  last-named  lies  one  of  the  longitudinal  excretory  tubes 
(ex.v).  The  nerve-cords  are  also  embedded  in  the  body-wall. 
The  intestine  consists  of  a  single  layer  of  columnar  cells,  the 
entoderm,  coated  both  within  and  without  by  a  thin  cuticle. 


der.  epthffv 


i?tt 


loll 


ex.v- 


Fig.  112  b.  —  Transverse  section  of  Ascaris  lumbric aides,  cu,  cuticle;  dl, 
dorsal  line;  der.epthm,  epidermis;  ex.v,  excretory  tube;  int,  intestine;  lal.l, 
lateral  line;  m,  muscular  layer;  ovy,'  ovary;  ut,  uterus;  v.v,  ventral  line. 
(From  Parker  and  Haswell,  after  Vogt  and  Yung.) 

The  coelom  (see  p.  89)  of  Ascaris  differs  from  that  of  the 
higher  animals  in  several  respects.  Typically  the  coelom  is  a 
cavity  in  the  mesoderm  lined  by  an  epithelium ;  into  it  the  ex- 
cretory  organs  open,  and  from  its  walls  the  reproductive  cells 
originate.  In  Ascaris  the  so-called  coelom  is  lined  only  by  the 
mesoderm  of  the  body- wall,  there  being  no  mesoderm  surround- 
ing the  intestine.  Furthermore,  the  excretory  organs  open  to 
the  exterior  through  the  excretory  pore,  and  the  reproductive 


PHYLUM  NEMATHELMINTHES  1 73 

cells  are  not  derived  from  the  coelomic  epithelium.  The  body- 
cavity  of  Ascaris,  therefore,  differs  structurally  and  functionally 
from  that  of  a  true  coelom,  but  nevertheless  is  similar  in  many 
respects. 

2.    NEMATHELMINTHES   IN    GENERAL 

Definition.  —  Phylum  Nemathelminthes.  —  Roundworms. 
—  Bilaterally  symmetrical,  triploblastic  animals  with  an  elon- 
gated cylindrical  body;  alimentary  canal  has  a  mouth  opening 
at  the  anterior  end  and  an  anal  opening  on  the  ventral  surface 
near  the  posterior  end,  and  lies  in  a  body-cavity,  which  is  prob- 
ably a  coelom;  no  cilia  present  in  any  part  of  the  body;  both 
free-living  and  parasitic;  sexes  separate. 

It  has  been  customary  to  place  the  Nematomorpha  (see  p. 
179)  and  Acanthocephala  (see  p.  180)  in  the  Phylum  Nemat- 
helminthes, but  the  relationships  of  these  animals  are  so  ob- 
scure that  it  is  considered  best  to  treat  them  separately.  The 
phylum,  therefore,  contains  only  one  class,  the  Nematoda, 
whose  members  have  all  of  the  characteristics  cited  above. 

Ascaris  lumhricoides  is  but  one  of  the  interesting  and  important 
nematodes.  It  belongs  with  a  number  of  other  similar  forms  to 
the  family  Ascarid^e. 

The  family  Strongylid^  contains  several  dangerous  para- 
sites. Ancylostoma  duodenalis,  the  European  hookworm,  is 
frequently  very  injurious  and  sometimes  fatal.  Nematodes  of 
this  species  are  taken  into  the  alimentary  canal  with  drinking 
water,  or  enter  the  body  through  the  skin,  and  thousands  are 
sometimes  present.  Anaemia  is  caused  by  their  biting  into  the 
intestinal  wall  and  destroying  the  capillaries.  Syngamus  is  the 
parasite  that  causes  the  disease  known  as  gapes  in  poultry 
and  game  birds.  The  birds  swallow  the  young  syngamids, 
which  soon  become  mature  in  the  trachea  and  bronchi. 

To  the  family  Trichinellid^  belongs  Trichinella  spiralis 
(Fig.  113)  which  causes  the  disease  of  human  beings,  pigs,  and 
rats  called  trichinosis.     The  parasites  enter  the  human  body 


174 


COLLEGE  ZOOLOGY 


Fig.  113.  —  Trichinella  spiralis  encysted 
among  muscle  fibers.  (From  Shipley  and 
MacBride,  after  Leuckart.) 


when  inadequately  cooked  meat  from  an  infected  pig  is  eaten. 
The  larvae  soon  become  mature  in  the  human  intestine,  and  each 
mature  worm  deposits  probably  about  10,000  young.  These 
young  are  either  placed  directly  into  the  lymphatics  by  the  female 

worms  or  burrow  through 

iji)^      ^  ' ^'liiL     the  intestinal  wall;  they 

encyst  in  muscular  tissue 
in  various  parts  of.  the 
body.  As  many  as  1 5 ,000 
encysted  parasites  have 
been  counted  in  a  single 
gram  of  muscle.  Pigs 
acquire  the  disease  by 
eating  offal  or  infested 
rats.  In  a  few  countries  pork  is  inspected  for  this  and  other 
parasites  by  government  agents. 

The  family  Filariid^e  is  also  important  because  of  the  human 
diseases  caused  by  certain  of  its  members.  The  most  injurious 
species  is  Filaria  bancrofti,  a  parasite  in  the  blood  of  man.  The 
larvae  of  this  species  are  about  j^q  inch  long.  During  the  day- 
time they  live  in  the  lungs  and  larger  arteries,  but  at  night  they 
migrate  to  the  blood-vessels  in  the  skin.  Mosquitoes,  which 
are  active  at  night,  suck  up  these  larvae  with  the  blood  of  the  in- 
fected person.  The  larvae  develop  in  the  mosquito's  body,  be- 
coming about  one  twentieth  of  an  inch  long;  make  their  way 
into  the  mouth  parts  of  the  insect;  and  enter  the  blood  of  the 
mosquito's  next  victim.  From  the  blood  they  enter  the  lym- 
phatics and  may  cause  serious  disturbances,  probably  by  ob- 
structing the  lymph  passages.  This  results  in  a  disease  called 
elephantiasis.  The  limbs  or  other  regions  of  the  body  swell  up 
to  an  enormous  size,  but  there  is  very  little  pain.  No  successful 
treatment  has  yet  been  discovered,  and  the  results  are  often  fatal. 
It  is  said  that  from  30  per  cent  to  40  per  cent  of  the  natives  of 
certain  South  Sea  Islands  are  more  or  less  seriously  afflicted. 
One  of  the  most  r^^gint  discoveries  with  regard  to  parasitic 


PHYLUM   NEMATHELMINTHES 


175 


roundworms  is  that  the  shiftlessness  of  the  "  poor  whites  "  of 
the  South  is  to  a  certain  degree  the  result  of  the  attack  of  the 
hookworm,  Necator  americanus.  The  larvae  of  the  hookworm 
develop  in  moist  earth  and  usually  find  their  way  into  the  bodies 
of  human  beings  by  boring  through  the  skin  of  the  foot.  In  the 
localities  where  the  hookworm  is  prevalent,  many  of  the  people 
go  barefoot.  The  larval  hookworms  enter  the  veins  and  pass  to 
the  heart;  from  the  heart  they  reach  the  lungs,  where  they  make 
their  way  through  the  air  passages  into  the  windpipe,  and  thence 
into  the  intestine.  To  the  walls  of  the  intestine  the  adults  at- 
tach themselves  and  feed  upon,  the  blood  of  their  host.  When 
the  intestinal  wall  is  punctured,  a  small  amount  of  poison  is 
poured  into  the  wound  by  the  worm.  This  poison  prevents  the 
blood  from  coagulating,  and  therefore  results  in  a  considerable 
loss  of  blood,  even  after  the  worm  has  left  the  wound.  The  vic- 
tims* of  the  hookworm  are  anaemic,  and  also  subject  to  tuber- 
culosis because  of  the  injury  to  the  lungs.  It  is  estimated  that 
2,000,000  persons  are  afflicted  by  this  parasite.  The  hook- 
worm disease  can  be  cured  by  thymol  (which  causes  the  worm  to 
loosen  its  hold)  followed  by  Epsom  salts.  The  most  important 
preventive  measure  is  the  disposing  of  human  faeces  in  rural 
districts,  mines,  brickyards,  etc.,  in  such  a  manner  as  to  avoid 
pollution  of  the  soil,  thus  giving  the  eggs  of  the  parasites  contained 
in  the  faeces  of  infested  human  beings  no  opportunity  to  hatch 
and  develop  to  the  infectious  larval  stage. 


CHAPTER   IX 

INVERTEBRATES    OF   MORE   OR   LESS   UNCERTAIN 
SYSTEMATIC   POSITION 


There  are  a  number  of  groups  of  animals  whose  relationships 
are  so  difficult  to  determine  that  authorities  do  not  agree  as 
regards  their  position  in  the  animal  series.  Most  of  these  groups 
contain  only  a  few  marine  species  which  are  of  very  little 
economic  importance.  A  few  groups  like  the  Rotifera  and 
Bryozoa  include  fresh-water  species  which  are  quite  common. 

I.   Mesozoa 

The  term  Mesozoa  (Gr.  mesos,  middle;  zoon,  animal)  has  been 
employed  by  a  number  of  zoologists  to  include  three  families  of 
parasites  of  obscure  systematic  position, 

(1)  theDlCYEMID^, 

(2)  the  Orthonec- 
TiD^E,  and  (3)  the 
Heterocyemid^. 
They  have  been 
regarded  as  inter- 
mediate between 
the  Protozoa  and 
Metazoa,  hence 
the  name  Mesozoa. 
It  is  probable,  how- 
ever, that  they  are 

Fig.  115.  — a  Meso-   degenerate    Meta- 
r.::  iFrdTedS   ^^^  dosely  alUed  to 

after  v.  Beneden.)  the  flatworms. 

176 


Fig.  114-  —  A  Meso- 
ZOON,  Dicyema  para- 
doxum.  (From  Parker 
and  Haswell,  after  Kol- 
Uker.) 


INVERTEBRATES  OF  UNCERTAIN  POSITION  177 

The  DiCYEMiD^  (Fig.  114)  and  Heterocyemid^  are  para- 
sites in  the  kidneys  of  Cephalopoda  (cuttlefishes  and  octopods). 
The  ORTHONE.CTiDiE  (Fig.  115)  are  parasites  in  Turbellaria 
(Chap.  VII),  Nemertinea,  Annelida  (Chap.  XI),  and  brittle- 
stars  (Ophiuroidea,  p.  199). 

2.  Nemertinea 

The  Nemertinea  (Gr.  nemertes,  true)  (Figs.  116,  117)  have  a 
superficial  resemblance  to  flatworms  and  are  by  some  authorities 
placed  in  the  Phylum  Platyhelminthes  either  as  a  distinct  class 
or  as  a  supplementary  group.  Some  of  them  are  very  long, 
reaching  a  length  of  ninety  feet.  A  few  species  live  in  moist  earth 
and  fresh  water,  but  most  of  them  are  marine.     Cerebratulus 


Fig.  116.  —  Micrura  verrilli,  one  of  the  Nemertinea  found  on  the 
Pacific  coast.     (From  Weysse,  after  Coe.) 

(Fig.  117)  and  Micrura  (Fig.  116)  are  marine;  Geonemertes  and 
some  species  of  Tetrastemma  are  terrestrial;  and  Malacohdella 
is  a  parasite  in  certain  mollusks. 

The  most  important  anatomical  features  of  the  Nemertinea 
are  the  presence  of:  (i)  a  long  proboscis  (Fig.  117,2, 10),  which  lies 
in  a  proboscis  sheath  just  above  the  digestive  tract,  and  may 
be  everted  and  used  as  a  tactile,  protective,  and  defensive  organ; 
(2)  a  hlood  vascular  system  consisting  usually  of  a  median  dorsal 
and  two  lateral  trunks  (Fig.  117,  9) ;  and  (3)  an  alimentary  canal 
with  both  mouth  (Fig.  117,  7)  and  anal  openings.  The  blood 
vascular  system  is  here  encountered  for  the  first  time.  Nemer- 
tinea possess  a  mesoderm  and  nervous  and  excretory  systems  which 
do  not  differ  markedly  from  those  of  the  flatworms.  The  pro- 
boscis sheath  may  represent  the  coelom,  but  this  is  not  certain. 

N 


178 


COLLEGE  ZOOLOGY 


Nemertines  feed  on  other  animals,  both  dead  and  alive.  They 
live,  as  a  rule,  coiled  up  in  burrows  in  the  mud  or  sand,  or  under 
stones,  but  some  of  them  frequent  patches  of  seaweed.  Loco- 
motion is  effected  by  the  cilia  which 
cover  the  surface  of  the  body,  by 
contractions  of  the  body  muscles, 
or  by  the  attachment  of  the  pro- 
boscis and  subsequent  drawing 
forward  of  the  body.  Cerehratulus 
(Fig.  117)  swims  actively  like  a 
leech  (Chap.  XI).  The  power  of 
regenerating  lost  parts  is  well 
developed. 

During  development  a  peculiar 
larval  stage  called  the  Filidium 
(Fig.  118),  is  usually  passed 
through.  This  resembles  a  helmet 
with  cilia   on   the   surface   and   a 


Fig.  117.  —  Cerehratulus  fus- 
cus,  a  Nemertine.  /,  cephalic 
slits ;  i,  opening  leading  into 
retracted  proboscis;  3,  dorsal 
commissure  of  nervous  system; 
4,  ventral  commissure;  5,  brain; 

6,  posterior     lobe     of     brain; 

7,  mouth;  8,  proboscis;  q,  lateral 
vessel;  /o,  proboscis;  j/,  pouches 
of  alimentary  canal;  12,  stomach. 
(From  Shipley  and  MacBride, 
after  Burger.) 


Fig.  1x8. — Pilidium  larva  of  a  Nemer- 
tine. D,  alimentary  canal;  E,  E',  the 
two  pairs  of  ectodermal  invaginations. 
(From  Sedgwick,  after  Metschnikoflf.) 


INVERTEBRATES  OF  UNCERTx\IN   POSITION 


179 


long' tuft  of  cilia  at  the  apex.  The  adult  develops  from  this 
larva  by  the  formation  of  ectodermal  invaginations  (Fig.  118, 
£,  E^)  which  surround-  the  alimentary  canal  {D).  This  in- 
vaginated  portion  escapes  from  the  Pilidium  and  grows  into 
the  adult  nemertine. 


3.  Nematomorpha 

This  group  (Gr.  nema,  thread;  morphe,  form)  contains  a  single 
family,  the  Gordiid^,  and  two  genera,  Gordius,  which  lives  in 
fresh  water,  and  Nedonema 
in  the  sea.  They  are  long, 
slender  thread-like  animals 
(Fig.  119)  often  found  in 
ditches  and  commonly  called 
horsehair  snakes.  Some 
authors  consider  them  an 
order  of  Nematoda;  whereas 
others  rank  them  as  a  class 
under    the   Phylum   Nemat- 

HELMINTHES.      It    SCCmS   bcst 

to  include  them  with  the 
other  invertebrates  of  more 
or  less  uncertain  systematic 
position. 

Their  resemblance  to  the 
Nematoda,  indicated  by  the 
term  Nem.a.tomorpha,  does  not  hold  for  the  internal  anatomy. 
A  distinct  epithelium  lines  the  body-cavity ;  no  lateral  lines  are 
present;  there  is  a  pharyngeal  nerve-ring  and  a  single  ventral 
nerve-cord;  and  the  ovaries,  which  are  segmentally  arranged, 
discharge  the  eggs  into  the  body-cavity. 

The  larvae  of  Gordius  usually  migrate  into  the  immature 
stages  of  aquatic  insects;  these  are  then  devoured  by  other 
animals  in  whose  intestines  the  young  live  and  develop  until 
they  finally  escape  into  the  water. 


a,  a. 


Fig.  119.  —  Gordius  (of 
Nematomorpha)  twining 
water-plant  and  laying  eggs, 
and  string  of  eggs.  (From  the  Cam- 
bridge Natural  History,  after  von 
Linstow.) 


the    group 

around     a 

clump 


i8o 


COLLEGE  ZOOLOGY 


4.  ACANTHOCEPHALA 

The  ACANTHOCEPHALA  (Gr.  akantha,  a  spine;  kephale,  the 
head)  are  parasitic  worms  which  are  also  considered  by  many 
a  class  in  the  Phylum  Nemathelminthes. 
They  are  spineheaded  worms  which  fasten 
themselves  to  the  intestinal  wall  of  verte- 
brates by  means  of  a  protrusible  proboscis 
covered  with  hooks  (Fig.  120,  R).  The 
presence  of  this  proboscis,  and  of  a  com- 
plex  reproductive  system,  and  the  absence 
of  an  alimentary  canal,  distinguish  the 
ACANTHOCEPHALA  from  the  Nematoda 
and  Nematomorpha. 

The  adults  are  most  common  in  fishes, 
but  all  vertebrates,  including  man,  are 
parasitized  by  them.     There  is  an  alterna- 


tion of  hosts  during  development.  For 
example,  the  larva  of  Echinorhynchus 
gigas  lives  in  the  June  bug,  the  adult  in 
the  pig. 

t;.    CHiETOGNATHA 


Fig.  120.  —  Echino- 
rhyncus  augustatus  (of 
the  group  Acantho- 
cephala),  male.  B,  re- 
tracted bursa;  De,  ejacu- 
latory  duct ;  G,  gang- 
lion;      Li,    ligament; 

P,  penis;  Pr,  prostatic  j^  Sagitta,  the  arrow-worm.     Figure   121 

sacs;     R,    proboscis;  °        '  ® 

Rs,  sheath  of  proboscis;  shows  most  of  the  anatomical  features  of 


The  Ch^etognatha  (Gr.  chaite,  horse- 
hair ;  gnathos,  the  cheek)  are  marine 
animals  which  swim  about  near  the  sur- 
face of  the-  sea.     The  best-known  genus 


rnt\l''''(From''sedgwkk"  '^^^^^^^   hexaptera.      There    is    a    distinct 
after  Leuckart.)  coslom,  an  alimentary  canal  with  mouth  (a), 

intestine  (b),  and  anus  (c),  a  well-developed 
nervous  system,  two  eyes,  and  other  sensory  organs.  The  mouth 
has  a  lobe  on  either  side  provided  with  bristles  (e)  which  are 
used  in  capturing  the  minute  animals  and  plants  that  serve  as 


INVERTEBRATES   OF  UNCERTAIN  POSITION 


l8l 


food.  The  members  of  the  group  are  hermaphroditic,  possessing 
both  male  and  female  reproductive  organs. 
The  CiLETOGNATHA  are  included  under 
the  Nemathelminthes  by  some  authori- 
ties and  are  placed  in  a  separate  phylum 
by  others.  ** 

6.  RoTiFERA  (Rotatoria) 

The  Rotifer  A  (Lat.  rota,  a  wheel ;  fero, 
I  carry)  (Fig.  122),  commonly  known  as 
wheel  animalcules,  are  extremely  small 
Metazoa.  They  were  at  one  time  con- 
sidered Infusoria.  Most  of  them  are 
inhabitants  of  fresh  water,  but  some  are 
marine  and  a  few  parasitic.  The  anatomy 
of  a  Rotifer  is  shown  in  Figure  123. 
The  head  is  provided  with  cilia  (c^  c^) 
which  aid  in  locomotion  and  draw  food 
into  the  mouth  {mth).  The  tail  or  foot  is 
bifurcated  and  adheres  to  objects  by  means 
of  a  secretion  from  a  cement  gland  {c.gl). 
The  body  is  usually  cylindrical  and  is 
covered  by  a  shell-like  cuticle  (cu). 

The  Protozoa  and  other  minute 
organisms  used  as  food  are  swept  by  the 
cilia  through  the  mouth  (mth)  into  the 
pharynx  (ph),  also  called  the  mastax  or 
chewing  stomach.  Here  chitinous  jaws, 
which  are  constantly  at  work,  break  up 
the  food.  The  movements  of  these  jaws 
easily  distinguish  a  living  rotifer  from 
other  organisms.  The  food  is  digested  in 
the  glandular  stomach  (st).  Undigested 
particles  pass  through  the  intestine  (int) 
into  the  cloaca  icl)  and  out  of  the  anus  (a). 


Fig.  121. — The  arrow- 
worm,  Sagilta  hexaptera 
(of  the  group  Ch.etoG' 
natha),  ventral  view, 
a,  mouth ;  b,  intestine  ; 
c,  anus;  d,  ventral  gang- 
lion; e,  movable  bristles 
on  the  head  ;  /,  spines  on 
the  head;  ^,  ovary;  /?,  ovi- 
duct ;  i,  vas  deferens ; 
j,  testis:  k,  seminal  vesicle, 
(From  Shipley  and  Mac- 
Bride,  after  Hertwig.) 


l82 


COLLEGE  ZOOLOGY 


Two  coiled  tubes  {nph),  which 
give  off  a  number  of  ciliated 
lobules  {fl.c),  and  enter  a 
bladder  {c.v),  constitute  the  ex- 
cretory  system.  The  bladder  con- 
tracts at  intervals,  forcing  the 
contents  out  of  the  anus.  Since 
the  amount  of  fluid  expelled  by 
the  bladder  is  very  large,  it  is 
probable  that  respiration  is  also 
a  function  of  this  organ,  the 
oxygen  being  taken  into  the 
animal  with  the  water  which 
diffuses  through  the  body-w^all. 
Two  species  of  Ro-  ^^^  the  carbonic  acid  being  cast 
TiFERA.    A,  Philodina.     B,  Hyda-    out    with    the    excretory    fluid. 

tina.     (From  Parker  and    Haswell,     rTy^        ^      ^  '^       • 

after  Hudson  and  Gosse.)  The   body-cavity  IS  not  a  true 

coelom. 
The  sexes  of  rotifers  are  separate.     The  female  possesses  an 
ovary  (Fig.  123,  ovy)  in  which  the  eggs  arise,  a  yolk-gland  (vt) 
which  supplies  the  eggs  with  yolk,  and  an  oviduct  (ovd)  which 


Fig.  123.^ — Diagram  showing  the  anatomy  of  a  Rotifer. 
a,  anus;  br,  brain;  c',  preoral,  and  c^,  postoral  circlet  of  cilia  ;\ 
c.gl,  cement  gland;  cl,  cloaca;  d.ep,  dermic  epithelium;  d.f,  dorsal 
feeler ;  e,  eye ;  Jl.c,  flame-cells ;  ini,  intestine ;  w,  muscles ;  mth,  mouth ; 
nph,  nephridial  tube;  ov,  ovum;  ovd,  oviduct;  ovy,  germarium;  ph,  pharynx; 
St,  stomach;   vt,  vitellarium.     (From  Parker  and  Haswell.) 


INVERTEBRATES   OF  UNCERTAIN   POSITION  183 

carries  the  eggs  (ov)  into  the  cloaca  (d).  From  here  the  eggs 
reach  the  exterior  through  the  anus.  The  males  are  usually 
smaller  than  the  females,  and  often  degenerate.  They  possess 
a  testis  in  which  the  spermatozoa  arise,  and  a  penis  for  trans- 
ferring the  spermatozoa  to  the  female. 

Two  kinds  of  eggs  are  produced  by  rotifers:  (i)  summer 
eggs,  and  (2)  winter  eggs.  The  summer  esss,  which  develop 
parthenogenetically,  are  thin-shelled,  and  of  two  sizes;  the 
larger  produce  females  and  the  smaller  males.  The  winter 
egg5,  which  are  fertilized,  have  thick  shells,  and  develop 
females. 

One  peculiarity  of  the  rotifers  worth  mentioning  is  their 
power  to  resist  desiccation.  Certain  species,  if  dried  slowly, 
secrete  gelatinous  envelopes  which  prevent  further  drying;  in 
this  condition  they  live  through. seasons  of  drought,  and  may  be 
subjected  to  extremes  of  temperature  without  perishing. 

The  resemblances  between  rotifers  and  the  trochophore 
larvae  of  certain  moUusks,  annelids,  and  other  animals  to  be 
described  later,  is  quite  striking.  The  larva  of  the  Nemertinea 
(Pilidium,  Fig.  118)  is  likewise  similar  in  some  respects  to  an 
adult  rotifer.  This  has  led  to  the  theory  that  the  rotifers  are 
animals  somewhat  closely  connected  with  the  ancestors  of  the 
moUusks,  annelids,  and  certain  other  groups. 

7.   Bryozoa  (Polyzoa) 

TheBRYOZOA  (Gr.  bruon, moss;  zoon,  an  animal),  Phoronidea, 
and  Brachiopoda  are  sometimes  placed  together  under  one 
phylum,  the  Molluscoidea,  because  they  are  moUusk-like  in 
form.  It  seems  probable,  however,  that  they  not  only  repre- 
sent distinct,  but  widely  divergent  groups,  and  should  therefore 
be  discussed  separately. 

The  Bryozoa,  or  moss-animals,  are  mostlv  colonial.  They 
resemble  hydroids,  like  Obelia  (Fig.  73),  in  form,  but  differ  from 
them  markedly  in  structure.  The  majority  of  them  live  in 
the  sea,  but  a  few  inhabit  fresh  water.     Bugula  (Fig.  124)  is 


1 84 


COLLEGE  ZOOLOGY 


a  common  marine  genus  which  shows  the  principal  characteristics 
of  the  group. 

The  soft  parts  constituting  the  polypide  lie  within  the  true 
coelomic  cavity  bounded  by  the  body-wall  or  zooecium.  The 
mouth  lies  in  the  midst  of  a  crown  of  ciliated  tentacles  (Fig.  124) 

called  the  lophophore,  which  serve  to 
draw  food  particles  into  the  body. 
The  U-shaped  alimentary  canal  con- 
sists of  a  ciliated  oesophagus  {Oes),  a 
stomach  (D),  and' an  intestine  which 
opens  by  means  of  an  anus  lying 
just  outside  the  lophophore.  One 
retractor  muscle  (R)  serves  to  draw 
the  polypide  into  the  zooecium.  The 
funiculus  (F)  is  a  strand  of  meso- 
dermal tissue  attached  to  the  base 
of  the  stomach.  There  are  no  circu- 
latory nor  excretory  organs. 

Both   an   ovary  and   a   testis   are 
present    in    each    individual ;    they 
may  be  found   attached  to  the  fu- 
niculus or  the  body-wall.     The  eggs 
are  probably  fertilized  in  the  ccelom 
and    then    develop   in    a    modified 
portion  of   the  zooecium  called   the 
ocecium  (Fig.  124,  Ovz).     The  larvae 
of  some  Bryozoa  resemble  a  trocho- 
phore  (see  p.  183). 
Certain  members  of  Bugula  colonies  are  modified  into  struc- 
tures called  avicularicB  (Fig.  124,  Av).    These  have  jaws  which 
probably  protect  the  colony  from  the  attacks  of  small  organisms 
and  prevent  the  larvae  of  other  animals  from  settling  upon  it. 

The  Bryozoa  may  be  separated  into  two  distinct  groups,  the 
EcTOPROCTA  and  Entoprocta.  In  the  former  the  anus  opens 
outside  of  the  lophophore,  as  in  Bugula,  and  a  coelom  is  present. 


Fig.  124.  —  Bugula  avicu- 
laria,  a  Bryozoon.  Av,  avicu- 
laria;  D,  alimentary  canal; 
F,  funiculus;  Oes,  oesophagus; 
Ovz,  ovicells;  R,  retractor 
muscle;  Te,  tentacular  crown. 
(From  Sedgwick,  after  v.  Nord- 
mann.) 


INVERTEBRATES   OF   UNCERTAIN   POSITION 


185 


Plumatella  and  Pectinatella  are  fresh-water 
EcTOPROCTA.  The  Entoprocta  have  the 
anal  opening  within  the  lophophore,  and 
the  space  between  the  intestine  and  body- 
wall  is  filled  with  mesoderm  cells.  Pedicel- 
Una  and  Urnatella  belong  to  this  giroup. 

8.  Phoronidea 
This  group  consists  of  a  single  genus, 
Phoronis  (Gr.  Phoronis,  name  of  a  king, 
Fig.  125),  containing  worm-like  animals 
which  live  in  the  sand,  enclosed  in  mem- 
branous tubes.  Their  systematic  position 
is  still  more  or  less  uncertain,  but  their 
structure  indicates  a  probable  relationship 
to  the  Ectoprocta. 


Fig.  125.  —  Phoronis 
bus  kit  (of  the  group 
Phoronidea)  removed 
from  its  tube  and  seen 
from  behind.  (From 
Sedgwick,  after  M'ln- 
tosh.) 


9,   Brachiopoda 
The    Brachiopoda    (Gr.    brachion,    the 
arm;    pous,    a   foot)   are   marine   animals 
living  within  a  calcareous  bivalve  shell  (Fig.  126).     They  are 
usually  attached  to  some  object  by  a  peduncle  (Fig.  127,  10). 


UTL 


Fig.  126.  —  Magellania  Jlavescens  (of  the  group  Brachiopoda).  A,  dorsal 
aspect  of  shell.  B,  shell  as  seen  from  the  left  side.  b,  beak;  d.v.,  dorsal  valve; 
/,  foramen;  v.v.,  ventral  valve.     (From  Weysse,  after  Davidson.) 


I 86  COLLEGE  ZOOLOGY 

Because  of  their  shell  they  were  for  a  long  time  regarded 
as  moUusks.  The  valves  of  the  shell,  however,  are  dorsal 
(Fig.  126,  d.v.)  and  ventral  (v.v.)  instead  of  lateral  as  in  the 
bivalve  mollusks  (Fig.  173).  Within  the  shell  (Fig.  127)  is 
a  conspicuous  structure  called  the  lophophore  (2),  which  consists 
of  two  coiled  ridges,  called  arms;    these  bear  ciliated  tentacles 


Fig.  127.  —  Anatomy  of  a  Brachiopod,  Waldheimia  australis.  i,  mouth; 
2,  lophophore;  3,  stomach;  4,  liver  tubes;  5,  median  ridge  on  shell;  6,  heart; 
7,  intestine;  8,  muscle  from  dorsal  valve  of  shell  to  stalk;  q,  opening  of  nephrid- 
ium;  10,  stalk;  //,  body-wall;  12,  tentacles;  13,  coil  of  lip;  14,  terminal 
tentacles.     (From  Shipley  and  MacBride.) 

(12).  Food  is  drawn  into  the  mouth  (i)  by  the  lophophore.  A 
true  coelo7n  is  present,  within  which  lie  the  stomach  (j),  digestive 
gland  {4),  and  the  heart  (6). 

The  group  Brachiopoda  is  extremely  old,  and,  although  found 
in  all  seas  to-day,  brachiopods  were  formerly  more  numerous  in 
species  and  of  much  greater  variety  in  form  than  at  present. 
Some  of  them,  for  example  Lingula,  are  apparently  the  same 
to-day  as  they  were  in  the  Silurian  period  estimated  at  about 
twenty-five  million  years  ago. 

lo.   Gephyrea 
The  Gephyrea  (Gr.  gephura,  a  mound)  are  worm-like  animals 
that  have  been  classed  by  many  zoologists  with  the  Phylum 
Annelida  (Chap,    XI).    Their  relations  to  this  phylum  are, 


INVERTEBRATES   OF   UNCERTAIN   POSITION 


187 


however,  uncertain,  and  the  affinities  of  the  Gephyrea  to  one 
another  are  even  doubtful.  Consequently  they  have  been 
separated  provisionally  from  the  Annelida  and  divided  into 
three  groups  as  follows:  — 

(i)  The  Echiuroidea  (Fig.   128)  have  traces  of  segmentation 
in  the  adult,  a  proboscis  (a),  a  pair  of  ventral  hooked  setce  (6), 


Fig.  128.  V^/  Fig.  129.  Fig.  130. 

Fig.  128.  —  Echiurus  pallasii  (of  the  group  Gephyrea).  a,  mouth  at  the 
end  of  the  grooved  proboscis;  b,  ventral  hooks;  c,  anus.  (From  the  Cam- 
bridge Natural  History.) 

Fig.  129. — Sipunculus  nudus  (of  the  group  Gephyrea)  laid  open  from  the 
side.  A,  anus;  BD,  brown  tubes  (nephridia);  D,  intestine;  G,  brain;  Te, 
tentacles;     VG,  ventral  nerve-cord.     (From  Sedgwick,  after  Keferstein.) 

Fig.  130.  —  Priapulus  caudatus  (of  the  group  Gephyrea).  a,  mouth 
surrounded  by  spines.     (From  the  Cambridge  Natural  History.) 

and  a  terminal  anus  (c).  They  usually  live  in  crevices  in  rocks, 
using  their  proboscis  for  locomotion,  for  capturing  prey,  and  as 
an  organ  of  sense.  There  is  a  trochophore  stage  (p.  183)  in 
development. 

(2)  The  Sipunculoidea  (Fig.  129)  are  unsegmented,  with  only 
one  pair  of  nephridia  (BD),  a  large  coelofn,  and  an  anus  (A)  on 


1 88  COLLEGE  ZOOLOGY 

the  dorsal  surface  near  the  anterior  end.  They  live  in  the  sand 
or  bore  into  coral  rock,  and  are  capable  of  slow,  creeping  loco- 
motion. The  anterior  part  of  the  body  can  be  drawn  into  the 
larger  posterior  portion,  and  is  therefore  called  the  introvert. 
Tentacles  (Te)  are  usually  present  at  the  anterior  end. 

(3)  The  Priapuloidea  (Fig.  130)  are  unsegmented,  with  an 
anterior  month  {a)  surrounded  by  chitinous  teeth,  and  a  posterior 
anus.  They  live  in  the  mud  or  sand  with  the  anterior  end 
projecting  from  the  surface. 


CHAPTER    X 
PHYLUM   ECHINODERMATAi 

The  Echinodermata  (Gr.  echinos,  a  sea-hedgehog;  derma, 
skin)  are  "  spiny-skinned  "  animals  that  live  in  the  sea.  They 
represent  the  most  complex  of  all  radially  symmetrical  animals. 
For  a  long  time  they  were  placed  with  the  Ccelenterata  in  a 
group  called  Radiata,  but  when  their  structure  and  life-history 
had  been  thoroughly  made  out,  they  were  found  to  have  closer 
aflSnities  with  the  higher  Metazoa. 

Five  classes  of  echinoderms  are  recognized  by  most  zoologists. 
Besides  these  there  are  several  groups  of  fossil  forms. 

Phylum  Echinodermata.  —  Starfishes,  Brittle-stars,  Sea- 
urchins,  Sea-cucumbers,  Sea-lilies.  Triploblastic,  radially 
symmetrical  animals ;  usually  five  antimeres,  ccelom  well 
developed;  anus  usually  present;  locomotion  in  many  species 
accomplished  by  characteristic  organs  known  as  tube-feet ;  a 
spiny  skeleton  of  calcareous  plates  generally  covers  the  body. 

Class  I.  Asteroidea  (Gr.  aster,  a  star;  eidos,  resemblance) 
(Fig.  131).  Typically  pentamerous;  arms  usually  not  sharply 
marked  off  from  the  disc ;  ambulacral  groove  present.  Ex- 
amples:  Asterias,  Astropecten,  Culcita.  —  Starfishes. 

Class  II.  Ophiuroidea  (Gr.  ophis,  a  snake;  oura,  a  tail; 
eidos,  form)  (Fig.  138).  Typically  pentamerous;  arms  sharply 
marked  off  from  the  disc;  no  ambulacral  groove.  Examples: 
Ophiura,  Amphiura,  Astrophyton.  —  Brittle-stars. 

Class  III.  EcHiNOiDEA  (Gr.  echinos,  hedgehog;  eidos,  form) 
(Fig.  141).     Pentamerous,  without  arms  or  free  rays;    test  of 

^  The  echinoderms  form  a  very  complex,  aberrant  coelomate  group,  and  their 
study  may  be  deferred  until  later  if  desirable. 

189 


I  go 


COLLEGE  ZOOLOGY 


calcareous  plates  bearing  movable  spines.  Examples:  CidariSj 
Arbacia,  Toxopneustes,  Strongylocentrotus.  —  Sea-urchins;  Echin- 
arachnius.  —  Sand-dollar;   Spatangus.  —  Heart-urchin. 

Class  IV.  HoLOTHURioiDEA  (Gr.  holos,  whole;  ihourioSj 
rushing)  (Fig.  146).  Long  ovoid;  muscular  body- wall ;  tentacles 
around  mouth.  Examples:  Holothuria,  Thy  one,  Caudina.  — 
Sea-cucumbers. 

Class  V.  Crinoidea  (Gr.  krinon,  a  lily;  eidos,  form)  (Fig. 
148).  Arms  generally  branched  and  with  pinnules;  aboral 
pole  usually  with  cirri  or  sometimes  with  stalk,  for  temporary 
or  permanent  attachment.  Examples:  Antedon.  —  Feather- 
star;  Pentacrinus.  —  Sea-lily. 

1.  Anatomy  and  Physiology  of  the  Starfish  —  Asterias 

External  Features.  —  The  starfishes  are  common  along  many 
sea-coasts,  where  they  may  be  found  usually  upon  the  rocks  with 

the  mouth  down. 
The  upper  surface 
is  therefore  ahoral 
or  ahactinal.  On 
the  ahoral  surface 
(Fig.  131)  are  (i) 
many  spines  (Fig. 
1 33  J  ^)  of  various 
sizes,  (2)  pedicel- 
larioe  (Fig.  133,  jo) 
at  the  base  of  the 
spines,  (3)  a  madre- 
porite  (Fig.  131, 
mad),  which  is  the 
entrance  to  the 
water-vascular 
system,    and     (4) 

Fig.  131.  —  The  starfish,  Asterias  ruhens,  seen  from  .1  j,„j,i  orkpnintr 
the  aboral  surface,  mad,  madreporite.  (From  the  ^"^  ^"^^  openmg' 
Cambridge  Natural  History.)  {auus).      A    glanCC 


.dorsal  spines 


PHYLUM   ECHINODERMATA 


191 


at  the  oral  surface  (Fig.  132)  reveals  a  mouth  centrally  situated 
in  the  membranous  peristome,  and  five  grooves  (ambulacral) ,  one 
in  each  arm,  from  which  two  or  four  rows  of  tube-feet  extend 
(Fig.  133,  77). 

The  Skeleton.  —  The  skeleton  is  made  up  of  calcareous  plates 
or  ossicles  bound  together  by  fib^ts  of  connective  tissue  (Fig. 
133,  Q,  II,  12).     The  ossicles  are  regularly  arranged  about  the 


Fig.  132. — A,  the  starfish,  Asterias  rubens,  seen  from  the  oral  surface. 
B,  an  adambulacral  spine,  showing  three  straight  pedicellarije.  C,  a  tube- 
foot  expanded  and  contracted.     (From  the  Cambridge  Natural  History.) 

mouth  and  in  the  ambulacral  grooves  and  often  along  the  sides 
of  the  arms,  but  are  more  or  less  scattered  elsewhere.  The  am- 
bulacral and  adambulacral  ossicles  (Fig.  133,  11,  12)  have  muscu- 
lar attachments  and  are  so  situated  that  when  the  animal  is 
disturbed  they  are  able  to  close  the  groove  and  thus  protect  the 
tube-feet.     The  spines  of  the  starfish  (Fig.  131;  Fig.  133,  8)  are 


192 


COLLEGE  ZOOLOGY 


short  and  blunt  and  covered  with  ectoderm  (Fig.  133,  j). 
Around  their  bases  are  many  whitish  modified  spines  called 
pedicellaricB  (Fig.  133,  10).  These  are  Uttle  jaws  which  when 
irritated  may  be  opened  and  closed  by  several  sets  of  muscles. 
Their  function  is  to  protect  the  dermal  hranchic^  (Fig.  133,  5), 
to  prevent  debris  and  small  organisms  from  collecting  on  the 


Fig.  133.  —  Diagram  of  a  transverse  section  of  the  arm  of  a  starfish. 
/,  ectoderm;  2,  jelly;  3,  peribranchial  space  in  the  skin;  4,  peritoneal  lining 
of  the  body-cavity;  5,  a  branchia;  6,  pyloric  caecum;  7,  mesentery  support- 
ing a  caecum;  8,  spine;  q,  ossicle  in  skin;  10,  pedicellaria;  11,  ambulacral 
ossicle;  12,  adambulacral  ossicle;  13,  radial  trunk  of  water-vascular  system; 
14,  radial  septum  separating  the  two  perihaemal  spaces;  15,  radial  nerve-cord; 
16,  ampulla  of  tube-foot;  17,  tube-foot;  18,  perihaemal  space;  iq,  coelom. 
(From  Shipley  and  MacBride.) 


surface,  and  to  capture  food.  The  skeleton  serves  to  give  the 
animal  definite  shape,  to  strengthen  the  body-wall,  and  as  a 
protection  from  the  action  of  waves  and  from  other  organisms. 

The  Muscular  System.  —  The  arms  of  the  starfish  are  not 
rigid,  but  may  be  flexed  slowly  by  a  few  muscle  fibers  in  the 
body-wall.     The  tube-feet  are  also  supplied  with  muscle  fibers. 

Coelom.  —  The  true  body-cavity  of  the  starfish  is  very  large 
and  may  be  separated  into  several  distinct  divisions.    The 


Pm^LUM   ECHINODERMATA 


193 


perivisceral  part  of  the  ccelom  (Fig.  133,  ig)  surrounds  the  ali- 
mentary canal  and  extends  into  the  arms.  It  is  lined  with 
peritoneum  (Fig.  133,  4)  and  filled  with  sea- water  containing 
some  albuminous  matter.  Oxygen  is  taken  into  the  coelomic 
fluid  and  carbon  dioxide  given  off  through  outpushings  of  the 
body- wall  known  as  papulce  or ^>-dermal  hranchice  (Fig.  133,  5). 
The  ccelom  also  has  an  ex- 
cretory function,  since  cells 
from  the  peritoneum  are 
budded  off  into  the  coelomic 
fluid,  where  they  move  about 
as  amoebocytes  gathering 
waste  matters.  These  cells 
make  their  way  into  the  der- 
mal branchiae,  through  the 
walls  of  which  they  pass  to 
the  outside,  where  they  dis- 
integrate. 

The  Water-vascular  Sys- 
tem. —  The  water- vascular 
system  (Fig.  134)  is  a  divi- 
sion of  the  coelom  peculiar  to 
echinoderms.  Beginning  with 
the  madreporite  (m)  the  fol- 
lowing structures  are  encoun- 
tered :  the  stone-canal  {m') 
running  downw^ards  enters 
the  ring-canal  {c),  which 
encircles  the  mouth;  from 
this  canal  five  radial  canals  (Fig.  134,  r;  Fig.  133,  ij),  one  in 
each  arm,  pass  outward  just  above  the  ambulacral  grooves.  The 
radial  canals  give  off  side  branches  from  which  arise  the  tube-feet 
(Fig.  134,  t;  Fig.  133,  ly)  and  ampullce  (Fig.  134,  a;  Fig.  133, 16.) 
The  ampullae  are  bulb-like  sacs  extending  into  the  coelom;  they 
are  connected  directly  w  ith  the  tube-feet,  which  pass  through  tiny 


Fig.  134.  —  Water-vascular  system  of 
a  starfish.  a,  ampullae ;  ap,  Polian 
vesicles ;  c,  circular  canal ;  m,  madre- 
porite; w',  madreporic  canal;  /,  tube-feet; 
r,  radial  canals ;  r',  branches  to  am- 
pullae. (From  Parker  and  Haswell,  after 
Gegenbaur.) 


194  COLLEGE  ZOOLOGY 

pores  between  the  ambulacral  ossicles  (Fig.  133,  11).  Sea-water 
is  forced  into  this  system  of  canals  by  cilia  which  occur  in  grooves 
on  the  outer  surface  of  the  madreporite  and  in  the  canals  which 
penetrate  it.  Arising  from  the  ring-canal  near  the  ampullae  of 
the  first  tube-feet  are  nine  vesicles  called,  after  the  name  of 
their  discoverer,  "  Tiedemann's  bodies."  These  structures  pro- 
duce amoebocytes  which  pass  into  the  fluid  of  the  water- 
vascular  system.  Polian  vesicles  (Fig.  134,  ap)  are  present  in 
some  starfishes,  but  not  in  Asterias. 

The  most  interesting  structures  of  the  water- vascular  system 
are  the  tube-feet.  They  are  primarily  locomotory  and  function 
as  follows:  "When  the  tube-foot  is  to  be  stretched  out,  the 
ampulla  contracts  and  drives  the  fluid  downwards.  The  con- 
traction of  the  ampulla  is  brought  about  by  muscles  running 
circularly  around  it.  The  tube-foot  is  thus  distended  and  its 
broad  flattened  end  is  brought  in  contact  with  the  surface  of 
the  stone  over  which  it  is  moving  and  is  pressed  close  against  it. 
The  muscles  of  the  tube-foot  itself,  which  are  arranged  longi- 
tudinally, now  commence  to  act,  and  the  pressure  of  the  water 
preventing  the  tearing  away  of  the  sucker  from  the  object  to 
which  it  adheres,  the  starfish  is  slowly  drawn  forward,  whilst 
the  fluid  in  the  tube-foot  flows  back  into  the  ampulla."  Tube- 
feet  are  also  sensory  (p.  197). 

A  number  of  other  spaces  and  canals  have  been  considered  as 
parts  of  the  coelom  and  at  one  time  were  supposed  to  be  a  "  blood"- 
vascular  system.  These  are  the  axial  sinus  lying  along  the 
stone-canal  and  opening  to  the  outside  through  the  madreporite, 
the  inner  circumoral  perihcemal  canal,  the  outer  perihcemal  canal 
beneath  the  ring-canal,  the  aboral  sinus,  and  the  perihranchial 
spaces.  The  functions  of  these  various  cavities  are  not 
clear. 

Digestion. — The  alimentary  canal  of  the  starfish  (Fig.  135) 
is  short  and  greatly  modified.  The  mouth  opens  into  an  oesoph- 
agus which  leads  into  a  thin-walled  sac,  the  stomach.  Follow- 
ing this  is  the  pyloric  sac.     From  the  pyloric  sac  a  tube  passes 


PHYLUM   ECHINODERMATA 


195 


into  each  arm,  then  divides  into  two  branches,  each  of  which 
possesses  a  large  number  of  lateral  pouches;  these  branches  are 
called  pyloric  or  hepatic  caca  (Fig.  135,  py).  They  are  green 
in  color.  Above  the  pyloric  sac  is  the  slender  rectum  (red.), 
which  may  open  to  the  outside  through  the  anus.  Two  branched 
pouches,  brown  in  color,  arise  frjpm  the  rectum  and  are  known 
as  rectal  cceca   {rect.ccec). 

The  food  of  the  starfish  consists  of   fish,  oysters,  mussels, 
barnacles,  clams,  snails,  worms,  Crustacea,  etc.     When  a  mussel 


'.    ax!  \  ,-' 

perih.         \  peristome 

Tierv.circ 

Fig.  135.  —  Diagrammatic  longitudinal  section  of  a  starfish,  ab.,  aboral 
sinus;  ax,  axial  sinus;  ax.',  inner  perihaemal  ring-canal;  br.,  branchia  or  gill; 
g.r,  genital  rachis;  tnp.,  madreporite;  musc.tr.,  muscle  uniting  ambulacral 
ossicles;  nerv.circ,  nerve-ring;  n.r.,  radial  nerve-cord;  oc,  eye-pit;  oss.,  ossicles 
in  skin;  p.br.,  peribranchial  sinus;  p.c,  pore  canal;  perih.,  (right)  perihaemal 
radial  canal,  (left)  outer  perihaemal  ring-canal;  py,  pyloric  caecum;  reel.,  rectum; 
rect.ccEC,  rectal  caeca;  sp.,  spines;  st.c,  stone-canal;  t,  tentacle  terminating 
radial  canal ;  w.v.r.,  water-vascular  radial  canal.  (From  the  Cambridge 
Natural  History.) 


is  to  be  eaten,  the  animal  seizes  it  with  the  tube-feet  "  and  places 
it  directly  under  its  mouth,  folding  its  arms  down  over  it  in  um- 
brella fashion  (Fig.  136).  The  muscles  which  run  around  the 
arms  and  disc  in  the  body-w^all  contract,  and  the  pressure  thus 
brought  to  bear  on  the  incompressible  fluid  contained  in  the 
coelom,  forces  out  the  thin  membranous  peristome  and  partially  • 
turns  the  stomach  inside  out.  The  everted  edge  of  the  stomach 
is  wrapped  round  the  prey.     Soon  the  bivalve  is  forced  to  relax 


196 


COLLEGE   ZOOLOGY 


...J^^% 


its  muscles  and  allow  the  valves  to  gape.  The  edge  of  the  stomach 
is  then  inserted  between  the  valves  and  applied  directly  to  the 
soft  parts  of  the  prey,  which  is  thus  completely  digested.  When 
the  starfish  moves  away,  nothing  but  the  cleaned  shell  is  left 
behind.  If  the  bivalve  is  small,  it  may  be  completely  taken  into 
the  stomach,  and  the  empty  shell  later  rejected  through  the 
mouth."  (MacBride.)  Schiemenz  has  shown  "  (i)  that 
whilst  a  bivalve  may  be  able  to  resist  a  sudden  pull  of  4000 
grammes  it  will  yield  to  a  pull  of  900  grammes  long  continued; 
(2)  that  a  starfish  can  exert  a  pull  of  1350  grammes;  (3)  that 
a  starfish  is  unable  to  open  a  bivalve  unless  it  be  allowed  to 

raise  itself  into  a  hump 
(Fig.  136)  so  that  the  pull 
of  the  central  tube-feet  is 
at  right  angles  to  the  prey. 
A  starfish  confined  between 
two  glass  plates  walked 
about  all  day  carrying  with 
it  a  bivalve  which  it  was 
unable  to  open."  (Mac- 
Bride.) 

Fig.  136.— View  of  starfish  (Echinaster)  The  lining  of  the  Stomach 
devouring  a  mussel  .  madreporite.  gecretCS  muCUS;  that  of  the 
(From  the  Cambridge  Natural  History.)  ,  ' 

pyloric  sac  and  caeca  secretes 
ferments;  these  change  proteids  into  diffusible  peptones,  starch 
into  maltose,  and  fats  into  fatty  acids  and  glycerine.  Thus  is 
digestion  accomplished.  Undigested  matter  is  ejected  through 
the  mouth,  and  very  little,  if  any,  matter  passes  out  of  the 
anus.  The  rectal  caeca  secrete  a  brownish  material  of  unknown 
function,  probably  excretory. 

Circulation.  —  The  fluid  in  the  ccelom  is  kept  in  motion  by 
cilia  and  carries  the  absorbed  food  to  all  parts  of  the  body. 

Excretion.  —  This  is  accomplished  by  the  amcebocytes  (neph- 
rocytes)  in  the  coelomic  fluid  (p.  193),  probably  aided  by  the 
rectal  caeca. 


•--  ^z.-,^..  ■ 


PHYLUM   ECHINODERMATA  197 

Respiration.  —  The  dermal  branchiae  (Fig.  133,  5)  function 
as  respiratory  organs  (p.  193). 

The  Nervous  System.  —  Besides  many  nerve-cells  which  lie 
among  the  ectoderm  cells,  there  are  ridges  of  nervous  tissue, 
the  radial  nerve-cords  (Fig.  135,  w.r.;  Fig.  133,  75),  running  along 
the  ambulacral  grooves,  and  unitifig  with  a  nerve-ring  (Fig.  135, 
nerv.circ)  encircling  the  mouth.  The  apical  nervous  system 
consists  of  a  trunk  in  each  arm  which  meets  the  other  trunks 
at  the  center  of  the  disc;  these  trunks  innervate  the  dorsal 
muscles  of  the  arms. 

Sense-organs.  —  The  tube-feet  are  the  principal  sense-organs. 
They  receive  nerve- fibers  from  the  radial  nerve-cords.  At  the 
end  of  each  radial  canal  (Fig.  135,  /)  the  radial  nerve-cord  ends 
in  a  pigmental  mass  (oc.) ;  this  is  called  the  eye,  since  it  is  a  light- 
perceiving  organ.  The  dermal  branchiae  are  probably  sensory, 
also. 

Reproduction.  —  The  sexes  of  starfishes  are  distinct.  The 
reproductive  organs  are  dendritic  structures,  two  in  the  base  of 
each  arm;  they  discharge  the  eggs  or  sperms  out  into  the  water 
through  pores  in  the  aboral  surface  at  the  interspace  between 
two  adjacent  arms.  The  eggs  of  many  starfishes  are  fertilized  in 
the  water;  they  are  holohlastic  (p.  87),  undergo  equal  cleavage^ 
and  form  a  blastula  and  gastrula  similar  to  those  shown  in 
Figure  51,  K,  M.  The  opening  (blastopore)  of  the  gastrula  be- 
comes the  anus,  and  a  new  opening,  the  mouth,  breaks  through. 
Ciliated  projections  develop  on  either  side  of  the  body,  and  a 
larva,  called  a  Bipinnaria  (Fig.  150,  B),  results.  This  changes 
(metamorphosis)  into  the  starfish. 

Behavior.  —  The  starfish  moves  from  place  to  place  by  means 
of  its  tube-feet  (p.  194).  During  the  day  it  usually  remains  quiet 
in  a  crevice,  but  at  night  it  is  most  active. 

The  responses  of  the  starfish  to  stimuli  are  too  complex  to 
be  stated  definitely.  When  a  starfish  is  placed  on  its  aboral 
surface  it  performs  the  ''  righting  reaction,"  i.e.  it  turns  a  sort 
of    handspring   by   means   of   its   arms.      Professor   Jennings 


198  COLLEGE   ZOOLOGY 

taught   individuals   to    use    a    certain    arm   in    turning   over.  ^ 
One  animal  was  trained  in  eighteen   days  (180  lessons),  and 
after  an  interval   of   seven   days   apparently  "  remembered " 
which  arm  to  use.     Old  individuals  could  not  be  trained  as 
readily  as  young  specimens. 

Regeneration.  —  The  starfish  has  remarkable  powers  of  re- 
generation. A  single  arm  with  part  of  the  disc  will  regenerate 
an  entire  body.  If  an  arm  is  injured,  it  is  usually  cast  off  near 
the  base  at  the  fourth  or  fifth  ambulacral  ossicle.  This  is 
autotomy  (see  also  pp.  117  and  155). 

Economic  Importance.  —  Oyster  beds  are  seriously  affected 
by  starfishes.  One  starfish  which  was  placed  in  a  dish  contain- 
ing clams  devoured  over  fifty  of  them  in  six  days.  Formerly 
starfishes  were  taken,  cut  in  two,  and  thrown  back;  this  of 
course  only  increased  the  number,  since  each  piece  regenerated 
an  entire  animal.  They  are  now  often  captured  in  a  mop-like 
tangle,  to  the  threads  of  which  the  pedicellariae  cling.  They  are 
then  thrown  out  on  the  shore  above  high-water  mark  and  left 
to  die  in  the  sun,  or  killed  in  hot  water. 

2.  Class  I.    Asteroidea  —  Starfishes 

Little  need  be  said  of  the  Asteroidea  beyond  what  has  been 
stated  above  concerning  one  of  the  common  species  of  the  wide- 
spread genus  Asterias.  The  number  of  arms  ranges  from  five 
to  more  than  forty,  but  aside  from  this  diversity  the  chief  dif- 
ferences in  shape  among  the  starfishes  are  brought  about  by 
the  variations  in  the  length  and  breadth  of  the  arms  and  by 
their  lateral  fusion.  In  some  cases  this  adhesion'  has  gone  so 
far  as  to  result  in  a  pentagonal  form  (Fig.  137).  The  skeleton 
differs  in  structure  in  different  species  and  is  of  importance  in 
classification. 

The  distinctive  characteristics  of  the  Asteroidea  are  as  fol- 
lows: Typically  pentamerous;  body  commonly  more  or  less 
flattened;    arms  long  or  short,  usually  not  sharply  marked  off 


PHYLUM   ECHINODERMATA 


199 


Fig.  137.  —  Pentaceros  reticularis,  oral  aspect.     A  lar^M   <tariish 
common,  on  the  coast  of  Florida.      (From  VVeysse.) 

from  disc;  viscera  extend  into  arms;  ambulacral  groove  on  ven- 
tral surface  of  arms;  anus  and  madreporite  dorsal. 

3.  Class  II.    Ophiuroidea  —  Brittle-stars 

Distinctive  Characteristics.  —  Body  flattened;  arms  distinct 
from  disc;  no  caeca  nor  gonads  in  arms;  no  ambulacral  grooves 
nor  anus;    madreporite  on  oral  surface. 

Structural  Peculiarities.  —  The  arms  of  the  brittle-stars  (Fig. 
138)  and  basket- fish  (Fig.  139)  are  noticeably  different  from 
those  of  the  starfish.  They  are  slender  and  exceedingly  flexible. 
The  ambulacral  groove  is  absent,  being  covered  over  by  skeletal 
plates  and  converted  into  the  epineural  canal.  Each  arm  is 
covered  by  four  rows  of  plates,  one  aboral,  one  oral,  and  two 
lateral.  Spines  are  restricted  to  the  lateral  plates.  Within  the 
arm  are  plates  which  have  fused  together  and  are  known  as 
vertebrce.     The  muscular  system  of  the  arm  is  well  developed. 


200  COLLEGE  ZOOLOGY 

The  water-vascular  system  differs  in  several  respects  from 
that  of  the  starfish.  The  madreporite  is  on  the  oral  surface. 
The  tube-feet  have  lost  their  locomotor  function  and  serve 
as  tactile  organs ;  the  ampullce  have  consequently  disap- 
peared. 

Nutrition.  —  The  food  of  the  brittle-stars  consists  of  minute 
organisms  and  decaying  organic  matter  lying  on  the  mud  of  the 
sea  bottom.     It  is  scooped  into  the  mouth  by  special  tube-feet, 


Fig.   138.  —  Aboral  view  of  Ophioglypha  bullata,  a  brittle-star.     (From 
Shipley  and  MacBride,  after  Thompson.) 

two  pairs  to  each  arm,  called  the  oral  tube-feet.  The  rows  of 
spines  which  extend  out  over  the  mouth  opening  serve  as  strainers 
(Fig.  140).  The  stomach  is  a  simple  sac  without  caeca;  it  can- 
not be  pushed  out  of  the  mouth.     There  is  no  anus. 

Behavior.  —  The  locomotion  of  brittle-stars  is  comparatively 
rapid.  The  arms  are  bent  laterally,  and  enable  animals 
belonging  to  certain  species  to  "  run,"  or  climb,  and 
probably  to  swim.  Apparently  they  cannot  be  taught  like 
starfishes. 


PHYLUM   ECHINODERMATA 


20I 


Fig.  139.  —  Aboral  view  of  a  basket-fish,   Astrophyton  linckii. 
(From  the  Cambridge  Natural  History,  after  Thompson.) 

Regeneration.  —  The  term  brittle-star  is  derived  from  the  fact 
that  these  animals  break 
off  their  arms  if  they  be- 
come injured.  This  auto- 
tomy  often  allows  the  in- 
dividual to  escape  from 
its  enemies,  and  is  of  no 
serious  consequence,  since 
new  arms  are  speedily 
regenerated.  In  a  num- 
ber of  species  the  aboral 
covering  of  the  disc  is 
normally  cast  off,  prob- 
ably for  reproductive  pur- 

FiG.    140.  —  Oral    view    of   Ophioglypha 
P^^^^*  bullata,    a    brittle-star.     (From    the    Cam- 

bridge Natural  History,  after  Thompson.) 


202  COLLEGE   ZOOLOGY 

4.   Class  III.    Echinoidea.  —  Sea-urchins 

Distinctive  Characteristics.  —  Pentamerous,  without  arms  or 
free  rays;  skeleton  usually  of  twenty  columns  of  firmly  united 
plates,  five  pairs  of  ambulacral  rows,  and  five  pairs  of  inter- 
ambulacral  rows. 

Structural  Peculiarities.  —  The  starfish  type  may  be  changed 
to  that  of  the  sea-urchin  quite  easily.     The  latter  (Figs.  141- 


FiG.   141.  —  Aboral  surface  of  a  sea-urchin,  Strongylocentrotus  drobachiensi?.     i,  ex- 
panded tube-feet;  2,  spines.     (From  Shipley  and  MacBride,  after  Agassiz.) 

142)  resembles  a  starfish  whose  aboral  surface  has  become 
exceedingly  reduced,  being  represented  by  a  small  area,  the 
periproct  (Fig.  142,  2),  and  the  tips  of  whose  arms  have  at  the 
same  time  been  bent  upward  and  united  near  the  center  of 
the  aboral  surface. 

The  skeleton  of  the  sea-urchin  is  known  as  a  shell  or  test,  and 
is  shown  in  detail  in  Figure  142.  The  apical  system  of  plates 
contains  the  madreporite  (j),  four  other  genital  plates  {4),  with 
genital  pores,  and  five  ocular  plates  (5) ,  each  with  a  mass  of  pig- 
mental cells.     There  are  five  pairs  of    columns  of    ambulacral 


PHYLUM   ECHINODERMATA 


203 


plates  (7),  so  called  because  they  are  penetrated  by  tube-feet  {8) 
and  five  pairs  of  columns  of  inter amhulacr at  plates  (6).  On  the 
inside  of  the  test  around  the  peristome  in  many  sea-urchins  are 
five  arches,  often  incomplete,  called  auricles.  Most  of  the  plates 
bear  spines  which  are  attached  by  muscles  and  move  freely  on 
little  knob-like  elevations  called  tubercles  (9).  The  pedicellaricB 
are  more  specialized  than  those  of  the  starfish;  they  commonly 


Fig.  142.  —  Dried  test  of  a  sea-urchin,  Echinus  esculentus.  i,  anus;  2,  peri- 
proct;  3,  madreporite;  4,  a  genital  plate;  5,  an  ocular  plate;  6,  an  interambu- 
lacral  plate ;  7,  an  ambulacral  plate ;  8,  pores  for  protrusion  of  tube-feet ; 
g,  tubercles  of  primary  spines.     (From  the  Cambridge  Natural  History.) 


have  three  jaws.  The  mouth  is  provided  with  five  white  teeth; 
these  are  part  of  a  complicated  structure  known  as  "  Aristotle's 
Lantern  "  (Fig.  143,  comp.,  eph.). 

Nutrition.  —  The  food  of  the  sea-urchin  consists  of  marine 
vegetable  and  animal  matter  which  is  ingested  by  means  of 
"  Aristotle's  Lantern."  The  intestine  (Fig.  143,  int)  is  very 
long;  it  takes  one  turn  around  the  inside  of  the  body  and  then 
bends  upon  itself  and  takes  a  turn  in  the  opposite  direction.  A 
small  tube,  the  siphon  (Fig.   143,  siph.),  accompanies  the  in- 


^04 


COLLEGE  ZOOLOGY 


testine  part  way,  opening  into  it  at  either  end.  The  anus 
(Fig.  142,  i)  of  the  sea-urchin  is  near  the  center  of  the  aboral 
surface. 

Respiration.  —  A  large  part  of  the  respiration  takes  place  in 
most  echinoids  through  ten  branched  pouches  situated  on  the  area 

comp.rel. 


oe  tooth  sac 

Fig.  143. — Internal  anatomy  of  a  sea-urchin,  Echinus  esculentus.  amp.,  am- 
pullae of  tube-feet;  car.,  auricle;  b.v.,  "  dorsal  blood-vessel  ";  comp.,  "  com- 
passes" of  Aristotle's  lantern;  comp.  eh.,  elevator  muscles;  comp.  ret.,  retractor 
muscles;  eph.,  epiphyses  of  jaws;  gon.,  gonad;  g.rach,  genital  rachis;  int,  in- 
testine; oe,  oesophagus;  prot.,  protractor  of  Aristotle's  lantern;  reel.,  rectum; 
ret.,  retractor  muscle;  siph.,  siphon;  st.,  stomach;  stone  c,  stone-canal.  (From 
the  Cambridge  Natural  History.) 


surrounding  the  mouth,  one  pair  in  each  angle  between  the 
ambulacral  plates.  The  tube-feet  also  are  respiratory  in 
function. 

Locomotion.  —  Both  tube-feet  and  spines  are  used  in  loco- 
motion. "  The  spines  are  pressed  against  the  substratum  and 
keep  the  animal  from  rolling  over  under  the  pull  of  the  tube- 
feet  and  also  help  to  push  it  on." 


PHYLUM   ECHINODERMATA 


205 


Echinoidea  in  General.  —  The  common  sea-urchins  just  de- 
scribed live  principally  on  rocky  shores.  The  cake-urchins 
(Fig.  144)  live  at  or  near  the  surface  of  the  sand;   a  common 

m.p 

pod' 


%^- 


pod 


Fig.  144.  —  Aboral  view  of  a  "  sand- 
dollar,"  Echinarachnius  parma.  m.p,  madre- 
porite;  pod,  small  tube-foot;  pod',  flattened 
respiratory  tube-foot.  (From  the  Cam- 
bridge Natural  History.) 


Fig.  145.  —  Aboral.  view 
of  the  test  of  a  heart- 
urchin,  Brissopsis  lyrifera. 
Af,  anus.  (From  Sedg- 
wick, after  Claus.) 


form  on  the  eastern  coast  of  North  America  is  the  sand-dollar, 
Echinarachnius.  The  heart-urchins  (Fig.  145)  bury  themselves 
in  the  mud  to  a  depth  of  from  a  few  inches  to  a  foot. 


5.   Class  IV.    Holothurioidea.  —  Sea-cucumbers 

Distinctive  Characteristics.  —  Elongated  on  principal  axis; 
body-wall  muscular  with  small  calcareous  plates;  contractile 
tentacles  around  mouth;    no  external  madreporite. 

Structural  Peculiarities.  —  The  most  striking  external  features 
of  the  sea-cucumber  (Fig.  146)  are  its  muscular  body-wall  almost 
devoid  of  large  skeletal  plates,  its  branching  tentacles  surrounding 
the  mouth,  and  its  lateral  position  when  at  rest  or  moving  about 
on  the  sea  bottom. 

The  water-vascular  system  (Fig.  147)  is  homologous  to  those 
of  the  other  classes  of  echinoderms.  There  is  a  circular  canal 
around  the  oesophagus  (2), -five  radial  canals  (i)  which   end 


2o6  COLLEGE   ZOOLOGY 

blindly  near  the  anus  (id),  and  tube-feet  (Fig.  146).  The  circular 
canal  (2)  gives  off  a  polian  vesicle  {4)  and  one  or  more  stone- 
canals  ending  in  internal  madreporites  {2$).  From  ten  to  thirty 
of  the  tube-feet  surrounding  the  mouth  are  modified  as  tentacles 
for  procuring  food. 

The  alimentary  canal  includes  a  long  looped  intestine  (Fig.  147, 
2 J,  8,  22),  the  posterior  end  of  which  is  a  muscular  enlargement 
called  the  cloaca  (ij).  Water  flows  into  the  cloaca  through  the 
anus  {16)  and  passes  into  two  long  branching  tubes,  the  respira- 
tory trees  (11,  ig) ;  here  part  of  it  probably  finds  its  way  through 


Fig.   146.  —  A  sea-cucumber,  Thyone  briareus,  partly  buried  in  mud. 
(From  Pearse  in  Biol.  Bui.) 

the  walls  into  the  body- cavity.  Respiration  is  carried  on  by  the 
cloaca,  respiratory  trees,  tentacles,  tube-feet,  and  body-wall. 
The  cloaca  and  respiratory  trees  also  function  as  excretory 
organs. 

Nutrition.  —  The  food  of  most  sea-cucumbers  consists  of 
organic  particles  extracted  from  the  sand  or  mud  which  is  taken 
into  the  alimentary  canal.  Some  species  are  said  to  stretch  out 
their  seaweed-like  tentacles  on  which  many  small  organisms 
come  to  rest.  "  When  one  tentacle  has  got  a  sufficient  freight 
it  is  bent  round  and  pushed  into  the  mouth,  which  is  closed 
on  it.  It  is  then  forcibly  drawn  out  through  the  closed  lips 
so  that  all  the  living  cargo  is  swept  off."  (Shipley  and 
MacBride.) 


PHYLUM   ECHINODERMATA 


207 


Behavior.  —  The 

tube-feet,  when  present, 
are  organs  of  locomotion. 
They  pull  the  animal 
along  on  its  ventral, 
flattened  surface. 
Waves  of  muscular  con- 
traction which  travel 
from  one  end  of  the 
body  to  the  other  are 
important  in  locomo- 
tion, and  the  tentacles 
may  also  assist. 

The  common  sea- 
cucumbers,  Thyone 
briareus,  are  sensitive 
to  contact  with  solid 
objects,  and  many  of 
them  burrow  in  the 
sand  or  mud.  They 
are  extremely  sensitive 
to  a  decrease  in  the 
light  intensity  and  will 
contract  the  body  if  an 
object  passes  between 
them  and  the  source  of 
light.  They  are  also 
negatively  phototropic, 
since  they  move  away 
from  the  light.  The 
following  has  been 
written  concerning  this 
species:  '' Passing  most 
of  its  life  buried  in  the 
mud,  Thyone  probably 


Fig.  147.  —  Internal  anatomy  of  a  sea- 
cucumber,  one  of  the  Aspidochirotce.  i,  radial 
vessel;  2,  water-vascular  ring;  3,  blood-vascular 
ring;  4,  Polian  vesicle;  5,  oesophagus;  6,  ventral 
blood-vessel  of  intestine;  7,  connecting  blood- 
vessel; 8,  second  part  of  intestine;  g,  10,  radial 
longitudinal  muscles;  11,  left  respiratory  tree; 
12,  dorsal-blood  vessel  of  intestine;  13,  circular 
muscles  of  body-wall;  14,  Cuvierian  organs; 
15,  cloaca;  16,  anus;  17,  radial  muscles  of 
cloaca;  18,  cut  edge  of  body- wall;  ig,  right 
respiratory  tree;  20,  posterior  edge  of  dorsal 
mesentery ;  21,  median  ventral  longitudinal 
muscles ;  22,  third  part  of  intestine ;  23,  first 
part  of  intestine;  24,  gonad;  25,  internal  madre- 
porites  of  two  stone-canals;  26,  dorsal  mesen- 
tery; 27,  genital  duct;  28,  interradial;  2q,  radial 
piece  of  calcareous  ring;  30,  genital  opening. 
(From  Sedgwick,  after  Leockart.) 


2o8  COLLEGE   ZOOLOGY 

does  not  often  fall  a  prey  to  large  enemies,  but  it  is  protected 
from  them  by  the  withdrawing  reaction,  by  its  locomotion  away 
from  the  light,  and  by  its  habit  of  pulling  eel  grass  and  other 
debris  over  the  body."     (Pearse.) 

Regeneration.  —  Sea-cucumbers  possess  remarkable  powers 
of  regeneration.  When  one  is  irritated  it  contracts  the  muscles 
of  the  body- wall,  and  "  since  the  fluid  in  the  body-cavity  is 
practically  incompressible,  the  effect  is  to  set  up  a  tremendous 
pressure.  As  a  result  of  this,  the  wall  of  the  intestine  near  the 
anus  tears,  and  a  portion  or  the  whole  of  the  intestine  is  pushed 
out.  The  gill  trees  are  the  first  to  go,  and  in  some  species  the 
lower  branches  of  these  are  covered  with  a  substance  which 
swells  up  in  sea-water  into  a  mass  of  tough  white  threads  in 
which  the  enemies  of  the  animal  are  entangled.  A  lobster  has 
been  rendered  perfectly  helpless  as  a  consequence  of  rashly  in- 
terfering with  a  sea-cucumber.  These  special  branches  are 
termed  Cuvierian  organs. 

"  A  Holothurioid  is  only  temporarily  inconvenienced  by  the 
loss  of  its  internal  organs.  After  a  period  of  quiescence  it  is 
again  furnished  with  the  intestine  and  its  appendages.  Some 
species,  which  are  able  to  pull  in  the  mouth  end  of  the  body  with 
their  tentacles,  when  strongly  irritated  snap  off  even  this,  and 
yet  are  able  to  repair  the  loss."     (Shipley  and  MacBride.) 

Economic  Importance.  —  Among  the  South  Pacific  islands 
and  on  the  coasts  of  Queensland  and  in  southern  China,  dried 
holothurians  are  known  as  "  beche-de-mer  "  or  "  trepang  "  and 
are  used  for  food.  The  trade  mounts  into  hundreds  of  thou- 
sands of  dollars  annually. 

6.   Class  V.    Crinoidea  —  Sea-lilies  or  Feather-stars 

Distinctive  Characteristics.  —  Attached  by  aboral  apex  of 
body  during  early  stages  of  development;  arms  usually  branched 
and  bearing  pinnules ;  tube-feet  like  tentacles,  without  ampullae. 

There  are  five  or  six  hundred  living  representatives  of  this  class; 
fossil  remains  are  very  abundant  in  limestone  formations.     Most 


PHYLUM   ECHINODERMATA 


209 


Fig.  148.  ^  A  crinoid,  Pentacrinus  maclearanus.  Anns  and 
portion  of  stem.  (From  the  Cambridge  Natural  History,  after 
Thompson.) 


of  the  living  crinoids  are 
found  at  moderate 
depths,  a  few  are  deep- 
sea  forms,  and  some 
inhabit  shallow  water. 
They  are  often  attached 
by  a  jointed  stalk. 
Some  species  break  off" 
from  the  stalk  when 
they  become  mature, 
and  probably  swim 
about  by  means  of  mus- 
cular contractions  of  the 
arms. 

The  arms  of  crinoids 
are  usually  five  in  num- 
ber. The  apparently 
greater  number  is  due  to 
branching  near  the  base 
p 


Fig.  i4g.  —  Fossil  Echinoderms.  A,  Theco- 
cystis  s(Bculus  (Thecoidea).  B,  Trochocystis 
bohemicus  (Carpoidea).  C,  Echinosphoerites 
aurantium  (Cystoidea).  D,  Granatocrinus 
(Blastoidea).  (A,  B,  C,  from  the  Cam- 
bridge Natural  History.  A  and  B,  after 
Jackel;'    C,  after  Zittel;    D,  from  Weysse.) 


210 


COLLEGE  ZOOLOGY 


(Fig.  148).  The  branches  may  be  equal,  or  one  large  and  the 
other  small;  in  the  latter  case  the  smaller  branch  is  called  a 
pinnule. 

Some  authors  place  the  class  Crinoidea  in  the  subphylum 
Pelmatozoa  along  with  four  classes  of  fossil  echinoderms,  the 
Thecoidea  (Fig.  149,  A),  Carpoidea  (Fig.  149,  B),  Cystoidea 
(Fig.  149,  C),  and  Blastoidea  (Fig.  149,  D). 

7.   Development  of  Echinoderms 

In  most  of  the  echinoderms,  the  eggs  pass  through  a  ciliated 
blastula  stage,  a  gastrula  stage,  and  a  larval  stage,  which,  in  the 


Fig.  150.  —  Larval  Echinoderms.  A,  a  young  larval  echinoderm.  coe,  coelom; 
int,  intestine;  oes,  oesophagus;  st,  stomach;  stom,  stomodaeum.  B,  a  larval 
Asteroid,  Bipinnaria  elegans.  i,  frontal  area;  2,  preoral  arm;  3,  anterior, 
4,  posterior  transverse  portion  of  ciliated  band;  5,  postoral;  6,  poster o-lateral; 
7,  postero-dorsal  arm;  8,  anal  area;  q,  oral  depression;  10,  antero-dorsal; 
II,  ventro-median,  12,  dorso-median  arm.  C,  a  larval  Ophiuroid  (Ophio- 
pluteus).  a,  anus;  d,  antero-lateral  arm;  d',  postero-lateral  arm;  e,  postoral 
arms;  g,  postero-dorsal  arm;  m,  mouth.  (A,  from  the  Cambridge  Natural 
History;  B  and  C,  from  Sedgwick, —  B,  after  Mortensen;   C,  after  Miiller.) 


course  of  from  two  weeks  to  two  months,  metamorphoses  into  an 
adult.  The  larvae  (Fig.  150,  A)  of  the  four  principal  classes  of 
echinoderms  resemble  one  another,  but  are  nevertheless  quite 
distinct.  They  are  bilaterally  symmetrical,  and  swim  about  by 
means  of  a  ciliated  band  which  may  be  complicated  by  a  number 
of  arm-like  processes.     The  alimentary  canal  consists  of  a  mouth 


PHYLUM   ECHINODERMATA 


211 


(Fig.  150,  A,  stom),  oesophagus  {oes),  stomach  (5/),  intestine 
{int),  and  anus.  From  the  digestive  tract  two  coelomic  sacs 
{coe)  are  budded  off ;  these  develop  into  the  body-cavity, 
water-vascular  system,  and  other  ccelomic  cavities  of  the 
adult. 

The  larvae  of  the  different  classes  have  been  given  names  as 
follows:  those  of  the  Asteroidea  are  called  Bipinnaria  (Fig. 
150,  B);  Ofbivroide A,  Ophiopluteus  (Fig.  150,  C);  Echinoidea, 


Fig.  151.  —  Larval  Echinoderms.  A,  a  larval  Echinoid  (Echinopluteus). 
z,  frontal  area;  2,  preoral  arm;  j,  postoral  arm;  4,  anterior;  5,  posterior  trans- 
verse portion  of  ciliated  band;  6,  unpaired  posterior  arm;  7,  anal  area; 
8,  postero-lateral  arm;  q,  oral  area;  10,  postero-dorsal  arm;  //,  antero-dorsal 
arm;    12,  antero-Iateral  arm. 

B,  a  larval  Holothurioid  {Auricidaria  stelligera).  i,  frontal  area;  2,  preoral 
process;  3,  anterior;  4,  posterior  portion  of  ciliated  band;  5,  postoral  process; 
6,  anal  area;  7,  postero-lateral  process;  8,  postero-dorsal  process;  g,  oral  de- 
pression; JO,  dorso-median  process;  11,  antero-dorsal  process.  (From  Sedg- 
wick, after  J.  MUller.) 


Echinopluteus  (Fig.  151,  A);  said  Holothuriotde A,  Auricularta 
(Fig.  151,  B).  The  adults  which  develop  from  these  larvae  are, 
as  we  have  seen,  radially  symmetrical,  although  many  of  them, 
notably  the  Holothurioidea,  are  more  or  less  bilateral  in  struc- 
ture. The  bilateral  condition  of  the  larvae  indicates  that  the 
ancestors  of  the  echinoderms  were  either  bilaterally  symmetrical 
or  that  the  larvae  have  become  adapted  to  an  active  life  in  the 
water. 


212  COLLEGE  ZOOLOGY 

8.   Artificial  Parthenogenesis 

The  eggs  of  echinoderms  pass  through  a  total  and  equal  cleav- 
age, and  are  easily  fertilized  and  reared  to  the  larval  stage  in 
the  laboratory.  For  these  reasons  they  have  become  classical 
material  for  embryological  studies  and  for  experimental  purposes. 

One  of  the  most  interesting  phenomena  discovered  by  means 
of  experiments  with  echinoderm  eggs  is  the  development  of  a 
larva  from  an  unfertilized  egg  when  subjected  to  certain  environ- 
mental conditions.  This  phenomenon  is  known  as  artificial 
parthenogenesis.  The  eggs  of  other  animals,  for  example  anne- 
lids, are  also  capable  of  developing  under  certain  conditions 
without  fertilization,  and  those  of  some  species,  like  plant  lice 
(Chap.  XIII)  and  rotifers  (p.  i8i),  are  normally  parthenogenetic, 
but  echinoderm  eggs  have  been  used  for  experimental  purposes 
more  frequently  than  any  others. 

Loeb  reared  normal  larvae  from  unfertilized  eggs  of  echino- 
derms by  immersing  them  in  solutions  such  as  chloride  of  sodium, 
potassium  bromide,  cane-sugar,  etc.  He  considered  the  in- 
creased osmotic  pressure  the  cause  of  development,  and  thought 
it  probable  that  in  ordinary  fertilization  the  spermatozoon  brings 
a  solution  with  a  high  osmotic  pressure  into  the  egg,  thereby 
causing  the  withdrawal  of  water.  Sea-water  concentrated  to 
70  per  cent  of  its  volume  has  a  similar  result.  A  lowering  of  the 
temperature  of  sea-water  to  the  freezing-point  causes  eggs  of 
Asterias  and  Arbacia  to  develop;  when  combined  with  a  chem- 
ical reagent,  a  higher  per  cent  of  blastulae  results.  Eggs  ex- 
posed to  a  higher  temperature  (35°  to  38°  C.)  during  the  early 
maturation  period  develop  parthenogenetically,  and  even  me- 
chanical agitation  may  have  a  similar  effect.  Normal  mitotic 
figures  appear  during  the  cleavage  of  these  eggs.  None  of  the 
larvae  thus  produced  was  reared  to  the  adult  stage. 

The  ease  with  which  echinoderm  eggs  can  be  handled  has  led 
to  some  experiments  that  have  an  important  bearing  upon  hered- 
ity.    Of  these  may  be  mentioned  the  fertilization  of  the  eggs  of 


PHYLUM    ECHINODERMATA  213 

one  species  with  the  spermatozoa  of  another  species,  and  the 
fertilization  of  enucleated  fragments  of  sea-urchins'  eggs  with 
spermatozoa  of  another  species. 

9.  The  Position  of  Echinoderms  in  the  Animal  Kingdom 

Echinoderms  and  coelenterates,  because  of  their  radial  sym- 
metry, were  at  onetime  placed  together  in  a  group  called  Radiata. 
The  anatomy  of  the  adult  and  the  structure  of  the  larvae,  how- 
ever, show  that  these  phyla  really  occupy  widely  separated  posi- 
tions in  the  animal  kingdom.     The  adult  echinoderms  cannot 

Blastoidea 

t 

Echinoidea      Holothurioidea  Cystoidea      Crinoidea 


Ophiuroidea      Protechinoidea  Carpoidea 

Asteroidea  Protopelmatozoa  (Thecoidea  ?) 


First  Fixed  Ancestor 

t 

Protocoelomata 

Fig.   152.  —  Diagram  showing  the  probable  relations  of  the  classes  of 
Echinoderms.     (After  MacBride.) 

be  compared  with  any  other  group  of  animals,  and  w^e  must  look 
to  the  larvae  for  signs  of  relationship.  The  bilateral  larva  is 
either  a  modification  for  a  free-swimming  life  or  an  indication 
of  the  condition  of  its  ancestors.  The  latter  view  is  accepted 
by  most  zoologists.  The  ancestors  of  echinoderms  were  doubt- 
less bilateral,  worm-like  animals  which  became  fixed  and  were 
then  modified  into  radially  symmetrical  adults.  The  probable 
relations  of  the  classes  of  echinoderms  are  shown  in  Figure  152 
(MacBride). 


214 


COLLEGE   ZOOLOGY 


It  is  interesting  to  compare  the  echinoderm  larva  with  that 
of  a  supposed  primitive  chordate,  the  Tornaria  of  Balanoglossus 
(Chap.  XIV,  Fig.  334).  The  remarkable  similarity  of  these 
larvai  suggests  that  chordates  (Chap.  XIV)  and  echinoderms 
may  have  had  the  same  or  similar  ancestors  (see  also  Chap. 
XXII). 


CHAPTER    XI 
PHYLUM    ANNELIDA 

The  annelids  (Lat.  annellus,  a  little  ring)  can,  in  most  cases, 
be  distinguished  from  other  worms,  like  Planaria  (Fig.  97)  and 
Ascaris  (Fig.  iii),  by  the  fact  that  the  body  is  divided  into  a 
number  of  similar  parts  called  segments,  metameres,  or  somites; 
these  are  arranged  in  a  linear  series  and  are  visible  externally 
because  of  the  grooves  which  encircle  the  body.  The  earth- 
worms and  leeches  are  well-known  examples.  Annelids  live  in 
fresh  water,  salt  water,  and  on  land;  some  are  parasitic  upon 
other  animals. 

The  Annelida  form  three  classes:  — 

(i)  Class  Archiannelida  (Gr.  arche,  beginning;  Lat.  annel- 
lus, a  little  ring)  (Fig.  162),  without  setae  (Fig.  153,  set)  or  para- 
podia  (Fig.  164,  para); 

(2)  Class  Ch^topoda  (Gr.  chaite,  bristle;  pons,  foot)  (Fig. 
163),  with  setae;   and 

(3)  Class  Hirudinea  (Lat.  hirudo,  a  leech),  without  setae 
or  parapodia,  but  with  suckers  (Fig.  169,  i,  2). 

I.  The  Earthworm  —  Lumbricus 

The  earthworm  has  been  for  many  yeats  and  is  still  a  favorite 
type  for  illustrating  the  anatomy  and  physiology  of  anneUds,  and 
for  teaching  general  zoological  principles^.  The  common  earth- 
worm, Lumbricus  terrestris,  lives  in  the  groimd  where  the  soil  is  not 
too  dry  or  sandy;  it  comes  to  the  surface  only  at  night  or  after  a 
rain.  In  many  parts  of  this  country  the  species  Allolohophora 
( Helodrilus)  longa  or  one  of  the  species  of  Diplocardia  are  more 
abundant  in  cultivated  soil  than  L.  terrestris. 

215 


2l6 


COLLEGE  ZOOLOGY 


External  Features. — The  body  of  Lumhricus  is  cylindroid, 
and  varies  in  length  from  about  six  inches  to  a  foot.  The  seg- 
ments, of  which  there  are  over  one  hundred,  are  easily  determined 
externally  because  of  the  grooves  extending  around  the  body. 

dors.Jr 


neph 


estTieph/ 


nephrost 


mco 


vent.v 


^ub.n.ress 


Fig.  153. — Transverse  section  through  the  middle  region  of  the  body  of 
the  earthworm,  Lumhricus.  circ.mus,  circular  muscle  fibers;  cael,  coelom; 
dors.v,  dorsal  vessel;  epid,  epidermis;  ext.neph,  nephridiopore;  hep,  chloro- 
gogen  cells;  long.mus,  longitudinal  muscles;  neph,  nephridium;  nephrost,  nephro- 
stome;  n.co,  nerve-cord;  set,  setae;  sub.n.vess,  subneural  vessel;  typh,  typhlo- 
sole;  vent.v,  ventral  vessel.  (From  Parker  and  Haswell,  after  Marshall  and 
Hurst.) 

At  the  anterior  end  a  fleshy  lobe,  the  prostomium  (Fig.  156,  i), 
projects  over  the  mouth  (5);  this  is  not  considered  a  true  seg- 
ment. It  is  customary  to  number  the  segments  with  roman 
numerals,  beginning  at  the  anterior  end,  since  both  external  and 
internal  structures  bear  a  constant  relation  to  them.     Segments 


PHYLUM  ANNELIDA  217 

XXXI  or  XXXII  to  XXXVII  are  swollen  in  mature  worms, 
forming  a  saddle-shaped  enlargement,  the  clitellum,  of  use  during 
reproduction.  Every  segment  except  the  first  and  last  bears 
four  pairs  of  /-shaped  chitinous  bristles,  the  setce,  situated  as 
indicated  in  Figure  153,  set;  thesa- may  be  moved  by  retractor 
and  protractor  muscles,  and  are  renewed  if  lost.  The  setae  on 
somite  XXVI  are  in  mature  worms  modified  for  reproductive 
purposes. 

The  body  is  covered  by  a  thin,  transparent  cuticle  (Fig.  153, 
cut)  secreted  by  the  cells  lying  just  beneath  it.  The  cuticle 
protects  the  body  from  physical  and  chemical  injury;  it  con- 
tains numerous  pores  to  allow  the  secretions  from  unicellular 
glands  to  pass  through,  and  is  marked  with  fine  strice,  causing 
the  surface  to  appear  iridescent. 

A  number  of  external  openings  of  various  sizes  allow  the  en- 
trance of  food  into  the  body,  and  the  exit  of  faeces,  excretory 
products,  reproductive  cells,  etc.  (i)  The  mouth  is  a  crescentic 
opening  situated  in  the  ventral  half  of  the  first  somite  (Fig.  156, 
5) ;  it  is  overhung  by  the  prostomium  (Fig.  156,  /).  (2)  The  oval 
anal  aperture  lies  in  the  last  somite.  (3)  The  openings  of  the 
sperm  ducts  or  vasa  deferentia  are  situated  one  on  either  side  of 
somite  XV.  They  have  swollen  lips;  a  slight  ridge  extends 
posteriorly  from  them  to  the  clitellum.  (4)  The  openings  of  the 
oviducts  are  small,  round  pores  one  on  either  side  of  somite  XIV; 
eggs  pass  out  of  the  body  through  them.  (5)  The  openings  of 
the  seminal  receptacles  appear  as  two  pairs  of  minute  pores  con- 
cealed within  the  grooves  which  separate  somites  IX  and  X, 
and  X  and  XL  (6)  A  pair  of  nephridiopores  (Fig.  153,  ex/,  neph.), 
the  external  apertures  of  the  excretory  organs,  open  on  every 
somite  except  the  first  three  and  the  last.  They  are  usually 
situated  immediately  anterior  to  the  outer  seta  of  the  inner  pair. 
(7)  The  body-cavity  or  ccelom  (Fig.  15;^  cosl.)  communicates 
with  the  exterior  by  means  of  dorsal  J>ores.  One  of  these  is  lo- 
cated in  the  mid-dorsal  line  at  the  anterior  edge  of  each  somite 
from  VIII  or  IX  to  the  posterior  end  of  the  body. 


2l8 


COLLEGE   ZOOLOGY 


General  Internal  Anatomy. 


If  a  specimen  is  cut  open  from 
the  anterior  to  the  pos- 
terior end  by  an  in- 
cision passing  through 
the  body- wall  a  trifle 
to  one  side  of  the  mid- 
dorsal  line,  a  general 
view  of  the  internal 
structures  may  be 
obtained  (Fig.  154). 
As  in  Ascaris  (p.  169, 
Fig.  112  b),  the  body 
is  essentially  a  double 
tube  (Fig.  153),  the 
body-wall  constitut- 
ing the  outer,  the 
straight  alimentary 
canal,  the  inner  ;  be- 
tween the  two  is  a  cav- 
ity, the  coelom  (coel). 
The  external  seg- 
mentation corresponds 
to  an  internal  division 
of  the  coelomic  cavity 
into  compartments  by 
means  of  partitions, 
called  septa  (Fig.  154), 
which  lie  beneath  the 
grooves.  These  septa 
are  absent  in  Ascaris. 
The  alimentary  canal 
passes  through  the 
center  of  the  body,  and 
is  suspended  in  the 
coelom  by  the  parti- 


PHYLUM   ANNELIDA  219 

tions.  Septa  are  absent  between  somites  I  and  II,  and  incom- 
plete between  somites  III  and  IV,  and  XVII  and  XVIII.  The 
walls  of  the  ccelom  are  lined  with  an  epithelium,  termed  the 
peritoneum.  The  coelomic  cavity  is  filled  with  a  colorless  fluid 
which  flows  from  one  compartmeAt  to  another  when  the  body 
of  the  worm  contracts.  In  somites  IX  to  XVI  are  the  repro- 
ductive organs  (Fig.  158);  running  along  the  upper  surface  of 
the  alimentary  canal  is  the  dorsal  blood-vessel  (Fig.  153,  dors.  v)\ 
and  just  beneath  it  lie  the  ventral  blood-vessels  {vent,  v)  and 
nerve-cord  {n.co). 

Detailed  Anatomy  and  Physiology.  —  Digestion.  —  The 
alimentary  canal  (Fig.  154)  consists  of  (i)  a  mouth  cavity  or  buccal 
pouch  in  somites  I  to  III,  (2)  a  thick  muscular  pharynx  (ph) 
lying  in  somites  IV  and  V,  (3)  a  narrow,  straight  tube,  the 
oesophagus  (oes),  which  extends  through  somites  VI  to  XIV, 
(4)  a  thin- walled  enlargement,  the  crop  or  proventriculus  (cr), 
in  somites  XV  and  XVI,  (5)  a  thick  muscular-walled  gizzard 
(giz)  in  somites  XVII  and  XVIII,  and  (6)  a  thin- walled  in- 
testine (int)  extending  from  somite  XIX  to  the  anal  aperture. 
The  intestine  is  not  a  simple  cylindrical  tube;  but  its  dorsal 
wall  is  infolded,  forming  an  internal  longitudinal  ridge,  the 
typhlosole  (Fig.  153,  typh).  This  increases  the  digestive  surface. 
Surrounding  the  alimentary  canal  and  dorsal  blood-vessel  is  a 
layer  of  chlorogogen  cells  (Fig.  153,  hep).  The  functions  of  these 
cells  are  not  known  W\\h  certainty,  but  they  probably  aid  in  the 
elaboration  of  food  and  are  excretory.  Three  pairs  of  calciferous 
glands  lie  at  the  sides  of  the  oesophagus  (Fig.  154,  oes.  gl)  in  seg- 
ments X  to  XII ;  they  produce  carbonate  of  lime,  which  prob- 
ably neutralizes  acid  foods. 

The  food  of  the  earthworm  consists  principally  of  pieces  of 
leaves  and  other  vegetation,  particles  of  animal  matter,  and  soil. 
This  material  is  gathered  at  night.  At  this  time  the  worms  are 
active;  they  crawl  out  into  the  air,  and,  holding  fast  to  the  tops 
of  their  burrows  with  their  tails,  explore  the  neighborhood. 
Food  particles  are  drawn  into  the  buccal  cavity  by  suction  pro- 


2  20  COLLEGE   ZOOLOGY 

duced  when  the  pharyngeal  cavity  is  enlarged  by  the  contrac- 
tion of  the  muscles  which  extend  from  the  pharynx-  to  the  body- 
wall. 

In  the  pharynx,  the  food  receives  a  secretion  from  the  pharyn- 
geal glands;  it  then  passes  through  the  oesophagus  to  the  crop, 
where  it  is  stored  temporarily.  In  the  meantime  the  secretion 
from  the  calciferous  glands  in  the  oesophageal  walls  is  added, 
neutralizing  the  acids.  The  gizzard  is  a  grinding  organ;  in  it 
the  food  is  broken  up  into  minute  fragments  by  being  squeezed 
and  rolled  about.  Solid  particles,  such  as  grains  of  sand,  which 
are  frequently  swallowed,  probably  aid  in  this  grinding  process. 
The  food  then  passes  on  to  the  intestine,  where  most  of  the  diges- 
tion and  absorption  takes  place. 

Digestion  in  the  earthworm  is  very  similar  to  that  of  higher 
animals.  The  digestive  fluids  act  upon  proteids,  carbohydrates, 
and  fats;  in  them  are  special  chemical  compounds,  called  fer- 
ments or  enzymes,  which  break  up  complex  molecules  without 
themselves  becoming  changed  chemically.  The  three  most  im- 
portant enzymes  are:  (i)  trypsin,  which  dissolves  pro teid;  (2)  dias- 
tase, which  breaks  up  molecules  of  carbohydrates;  and  (3)  steap- 
sin,  which  acts  upon  fats.  These  three  enzymes  are  probably 
present  in  the  digestive  fluids  of  the  earthworm.  The  proteids 
are  changed  into  peptones,  the  carbohydrates  into  a  sugar  com- 
pound, and  the  fats  are  divided  into  glycerine  and  fatty  acids. 

The  food  is  now  ready  for  absorption.  This  is  accomplished 
through  the  wall  of  the  intestine  by  a  process  known  as  osmosis, 
assisted  by  an  ameboid  activity  of  some  of  the  epithelial  cells. 
^^-^'Osmosis  is  the  passage  of  a  liquid  through  a  membrane.  Upon 
reaching  the  blood,  the  absorbed  food  is  carried  to  various  parts 
of  the  body.  Absorbed  food  also  makes  its  way  into  the  ccelomic 
cavity  and^is^  carried  directly  to  those  tissues  bathed  by  the 
j^oelomic  fluid.  In  'one-celled  animals,  and  in  such  Metazoa 
as  Hydra,  Planaria,  and  Ascaris,  no  circulatory  system  is  neces- 
sary, since  the  food  either  is  digested  within  the  cells  or  comes 
into  direct  contact  with  them;   but  in  large,  complex  animals  a 


PHYLUM   ANNELIDA  221 

special  system  of  organs  must  be  provided  to  enable  the  proper 
distribution  of  nutriment. 

Circulation.  —  The  hlood  of  the  earthworm  is  contained  in 
a  comphcated  system  of  tubes  which  ramify  to  all  parts  of  the 
body.  A  number  of  these  tubes  a^e  large  and  centrally  located; 
these  give  off  branches  which  likewise  branch,  finally  ending  in 
exceedingly  thin  tubules,  the  capillaries.  The  functions  of  this 
system  of  tubes  are  to  carry  nourishment  from  the  alimentary 
canal  to  all  parts  of  the  body,  to  transport  waste  products,  and 
to  convey  the  blood  to  a  point  near  the  surface  of  the  body  where 
oxygen  may  be  obtained  and  supplied  to  the  tissues. 

The  hlood  of  the  earthworm  consists  of  a  plasma  in  which  are 
suspended  a  great  number  of  colorless  cells,  called  corpuscles. 
Its  red  color  is  due  to  a  pigment  termed  hcemoglobin  which  is 
dissolved  in  the  plasma.  In  vertebrates  the  haemoglobin  is 
located  in  the  blood  corpuscles. 

There  are  five  longitudinal  blood-vessels  connected  with  one 
another  and  with  various  organs  by  branches,  more  or  less  regu- 
larly arranged.  These  are  shown  in  Figure  155,  and  are  as 
follows:  (i)  the  dorsal  or  supra-intestinal  vessel  (sp),  (2)  the 
ventral  or  subintestinal  trunk  (sb.),  (3)  the  subneural  trunk  (sn), 
(4)  two  lateral  neural  trunks  (nl),  (5)  five  pairs  of  hearts  (ht) 
in  segments  VII  to  XI,  (6)  two  intestino-tegumentary  ves- 
sels {it  in  A  and  B)  arising  in  segment  X  and  extending  to  the 
oesophagus,  integument,  and  nephridia  in  segments  X  to  VI, 
(7)  branches  from  the  ventral  trunk  to  the  nephridia  and  body- 
wall  (D),  (8)  parietal  vessels  connecting  the  dorsal  and  sub- 
neural  trunks  in  the  intestinal  region,  (9)  branches  from  the 
dorsal  trunk  to  the  intestine,  (efi.  in  C),  (10)  a  typhlosolar  ves- 
sel connected  by  branches  with  the  intestine  and  dorsal  trunk, 
and  (11)  branches  from  the  ventral  vessel  to  the  nephridia  and 
body- wall  {sb.  in  D). 

The  dorsal  trunk  and  hearts  determine  the  direction  of  the 
blood  flow,  since  they  furnish  the  power  by  means  of  their 
muscular  walls.     Blood  is  forced  forward  by  wave-like  contrac- 


222 


COLLEGE   ZOOLOGY 


tions  of  the  dorsal  trunk,  beginning  at  the  posterior  end  and 
traveling  quickly  anteriorly.     These  contractions  are  said  to  be 


Fig.  155.  —  Diagrams  showing  the  arrangement  of  the  blood-vessels  in  the 
earthworm.  A,  longitudinal  view  of  the  vessels  in  somites  VIII,  IX,  and  X. 
B,  transverse  section  of  same  region.  C,  longitudinal  view  of  the  vessels  in 
the  intestinal  region.  D,  transverse  section  through  the  intestinal  region. 
af.i,  afferent  intestinal  vessel;  cv,  parietal  vessel;  ef.i,  efferent  intestinal 
vessel;  ht,  heart;  it,  intestine;  il,  intestino-tegumentary;  nl,  lateral-neural 
vessel ;  oe,  oesophagus ;  s,  septa ;  sh.,  ventral  vessel ;  sn.,  sub-neural  vessel ; 
sp.,  dorsal  vessel ;    ty.,  typhlosolar  vessel.      (From  Bourne,  after  Benham.) 

peristaltic^  and  have  been  likened  to  the  action  of  the  fingers  in 
the  operation  of  milking.  Valves  in  the  walls  of  the  dorsal  trunk 
prevent  the  return  of  blood  from  the  anterior  end.     In  somites 


PHYLUM  ANNELIDA  223 

VII  to  XI  the  blood  passes  from  the  dorsal  trunk  into  the  hearts^ 
and  is  forced  by  them  both  forward  and  backward  in  the  ventral 
trunk.  Valves  in  the  heart  also  prevent  the  backward  flow. 
From  the  ventral  trunk  the  blood  passes  to  the  body-wall  and 
nephridia.  Blood  is  returned  from  the  body-wall  to  the  lateral- 
neural  trunks.  The  flow  in  the  subneural  trunk  is  toward  the 
posterior  end,  then  upward  through  the  parietal  vessels  into  the 
dorsal  trunk.  The  anterior  region  receives  blood  from  the  dorsal 
and  ventral  trunks.  The  blood  which  is  carried  to  the  body- 
wall  and  integument  receives  oxygen  through  the  cuticle,  and 
is  then  returned  to  the  dorsal  trunk  by  way  of  the  subneural 
trunk  and  the  intestinal  connectives.  Because  of  its  proximity 
to  the  subneural  trunk,  the  nervous  system  receives  a  continu- 
ous supply  of  the  freshest  blood. 

Respiration.  —  The  earthworm  possesses  no  respiratory 
system,  but  obtains  oxygen  and  gets  rid  of  carbon  dioxide  through 
the  moist  outer  membrane.  Many  capillaries  lie  just  beneath 
the  cuticle,  making  the  exchange  of  gases  easy.  The  oxygen 
is  combined  with  the  haemoglobin. 

Excretion.  —  Most  of  the  excretory  matter  is  carried  out- 
side of  the  body  by  a  number  of  coiled  tubes,-  termed  nephridia 
(Fig.  153,  neph),  a  pair  of  which  are  present  in  every  somite 
except  the  first  three  and  the  last.  A  nephridium  occupies  part 
of  two  successive  somites ;  in  one  is  a  ciliated  funnel,  the  nephro- 
stome  (Fig.  153,  nephrost),  which  is  connected  by  a  thin  ciHated 
tube  with  the  major  portion  of  the  structure  in  the  somite 
posterior  to  it.  Three  loops  make  up  the  coiled  portion  of  the 
nephridium.  The  cilia  on  the  nephrostome  and  in  the  nephrid- 
ium create  a  current  which  draws  solid  waste  particles  from 
the  coelomic  fluid.  Glands  in  the  coiled  tube  take  waste  matter 
from  the  blood,  and  the  current  in  the  tube  carries  it  out  through 
the  nephridiopore  (ext.neph). 

Nervous  System.  —  The  nervous  system  differs  from  that  of 
the  types  studied  heretofore  in  being  more  concentrated. '  There 
is  a  bilobed  mass  of  nervous  tissue,  the  brain  or  suprapharyngeal 


224 


COLLEGE  ZOOLOGY 


ganglion,  on  the  dorsal  surface  of  the  pharynx  in  segment  III 
(Fig.  156,  2).  This  is  connected  by  two  circumpharyngeal 
connectives  (j)  with  a  pair  of  subpharyngeal  ganglia  which  Ue 
just  beneath  the  pharynx  (4).  From  the  latter  the  ventral  nerve- 
cord  (Fig.  154,  nx)  "extends  posteriorly  near  the  ventral  body- 
wall  (Fig.  153,  n.co).  The  ventral  nerve-cord  enlarges  into  a 
ganglion  in  each  segment  and  gives  off  three  pairs  of  nerves  in 

^  every  segment  pos- 

terior to  IV.  Each 
ganglion  really 
consists  of  two 
ganglia  fused  to- 
gether. Near  the 
dorsal  surface  of 
every  ganglionic 
mass  are  three 
longitudinal  cords, 
the  neurochords  or 
"  giant  fibers  '* 
(Fig.  157,  vg.). 
The  brain  and 
nerve-cord  con- 
stitute the  central 
nervous  systernj  the  nerves  which  pass  from  and  to  them  repre- 
sent the  peripheral  nervous  system. 

The  nerves  of  the  peripheral  nervous  system  are  either  efferent 
or  afferent.  Efferent  nerve- fibers  (Fig.  157,  mf.)  are  extensions 
from  cells  in  the  ganglia  of  the  central  nervous  system.  They 
pass  out  to  the  muscles  or  other  organs,  and,  since  impulses 
sent  along  them  give  rise  to  movements,  the  cells  of  which  they 
are  a  part  are  said  to  be  motor  nerve-cells  (mc).  The  afferent 
fibers  (sf.)  originate  from  nerve-cells  in  the  epidermis  (sc)  which 
are  sensory  in  function,  and  extend  into  the  ventral  nerve-cord. 
The  functions  of  nervous  tissue  are  perception,  conduction, 
and  stimulation.     These  are  usually  performed  by  nerve-cells, 


Fig.  156.  —  Diagram  of  the  anterior  end  of  an  earth- 
worm to  show  the  arrangement  of  the  nervous  system. 
/,  prostomium ;  2,  brain ;  3,  circumpharyngeal  connec- 
tive; 4,  subpharyngeal  ganglion;  5,  mouth;  <5,  pharynx; 
7,  setae ;  8,  tactile  nerves  to  prostomium ;  q,  dorsal 
nerves;  10,  ventral  nerves.  (From  Shipley  and  Mac- 
Bride.) 


PHYLUM  ANNELIDA 


225 


called  neurons.  The  neuron  theory  "  supposes  that  there  is  no 
nerve- fiber  independent  of  nerve-cell  and  that  the  cell  with  all 
its  prolongations  is  a  unit  or  a  neuron;  that  these  units  are  not 
united  to  one  another  anatomically,  but  act  together  physio- 
logically by  contact;  that  the  entire  nervous"  system  consists 
of  superimposed  neurons;  .  .  ."     (Barker.) 

The  reflex  carried  out  either  consciously  or  unconsciously  is 
considered  the  physiological  unit  of  nervous  activity.  The  ap- 
paratus required  for  a  simple  reflex  in  the  body  of  an  earthworm 


Fig.  157.  — Transverse  section  of  the  ventral  nerve  chain  and  surrounding 
structures  of  an  earthworm,  cm,  circular  muscles;  ep.,  epidermis;  Int.,  longi- 
tudinal muscles;  mc,  motor  cell  body;'  mf.,  motor  nerve-fiber;  sc,  sensory  cell 
body;  sf.,  sensory  nerve-fiber;  vg.,  ventral  ganglion.  (From  Parker  in  Pop. 
Sci.  Monthly,  modified  after  Retzius.) 

is  represented  in  Figure  157.  A  primary  sensory  neuron  {sc), 
lying  at  the  surface  of  the  body,  sends  a  fiber  {sf.)  into  the  ven- 
tral nerv^e-cord,  where  it  branches  out;  these  branches  are  in 
physiological  continuity  with  branches  from  a  primary  motor 
neuron  {mc.)  lying  in  the  ganglion  of  the  ventral  nerve-cord. 
The  second  neuron  {mc.)  sends  fibers  {mf.)  into  a  reacting  organ, 
which  in  this  case  is  a  muscle.  These  fibers  extending  to  the  re- 
acting organ  are  called  motor  fibers  {mf.);  those  leading  to  the 
ventral  nerve-cord  are  termed  sensory  fibers  {sf.).  The  first 
neuron,  or  receptor,  receives  the  stimulus  and  produces  the  nerve 
impulse;  the  second  neuron,  the  adjustor,  receives,  directs,  and 
modifies  the  impulse;  and  the  muscle  or  other  organ  stimulated 
Q 


226  COLLEGE  ZOOLOGY 

to  activity  is  the  efector.  Within  the  ventral  nerve-cord  are 
association  neurons  whose  fibers  serve  to  connect  structures 
within  one  ganglion  or  two  succeeding  ganglia.  These  short 
neurons  overlap  one  another,  and  are  doubtless  responsible  for 
the  muscular  waves  which  pass  from  the  anterior  to  the  posterior 
end  of  the  worm  during  locomotion.  The  three  giant  fibers, 
which  lie  in  the  dorsal  part  of  the  ventral  nerve-cord  throughout 
almost  its  entire  length,  are  connected  by  means  of  fibrils  with 
nerve-cells  in  the  ganglia,  and  probably  distribute  the  impulse 
that  causes  a  worm  to  contract  its  entire  body  when  strongly 
stimulated. 

Sense-organs.  —  The  sensitiveness  of  Lumbricus  to  light 
and  other  stimuli  is  due  to  the  presence  of  a  great  number  of 
epidermal  sense-organs.  These  are  groups  of  sense-cells  con- 
nected with  the  central  nervous  system  by  means  of  nerve- 
fibers  and  communicating  with  the  outside  world  through  sense- 
hairs  which  penetrate  the  cuticle.  More  of  these  sense-organs 
occur  at  the  anterior  and  posterior  ends  than  in  any  other  region 
of  the  body. 

Reproduction.  —  Both  male  and  female  sexual  organs  occur 
in  a  single  earthworm.  Figure  158  shows  diagrammatically 
the  position  and  shape  of  the  various  structures.  The  female 
system  consists  of:  (i)  a  pair  of  ovaries  (o)  in  segment  XIII;  (2) 
a  pair  of  oviducts  (od)  which  open  by  a  ciliated  funnel  in  seg- 
ment XIII,  enlarge  into  an  egg  sac  (R)  in  segment  XIV,  and 
then  open  to  the  exterior;  and  (3)  two  pairs  of  seminal  receptacles 
or  spermathecce  {s),  in  somites  IX  and  X.  The  male  organs  are 
(i)  two  pairs  of  glove-shaped  testes  (T)  in  segments  X  and  XI, 
(2)  two  vasa  defer entia  (vd)  which  lead  fronxciliatedHhmnels  (SF) 
to  the  exterior  in  segment  XV,  and  (3)  th^e  pairs  of  seminal 
vesicles  in  segments  IX  (A),  XI  (C),  and  XII,  and  two  central 
reservoirs  (B). 

Self-fertilization  does  not  take  place,  but  spermatozoa  are 
transferred  from  one  worm  to  another  during  a  process  called 
copulation.     Two  worms  come  together,  as  shown  in  Figure  159, 


PHYLUM   ANNELIDA 


227 


A;  slime  tubes  are  formed,  and  then  a  band-like  cocoon  is  secreted 
about  the  clitellar  region.     Eggs  and  spermatozoa  are  deposited 


.^=^-^^=^^a    ^ 


Fig.  158.  —  Diagram  of  the  reproductive  organs  of  the  earthworm,  dorsal 
view.  A,  B,  C,  seminal  vesicles;  N,  nerve-cord;  O,  ovary;  OD,  oviduct; 
R,  egg  sac;  S,  spermatheca;  SF,  seminal  funnel;  T,  testes;  VD,  vas  deferens. 
(From  Marshall  and  Hurst.) 


in  the  cocoon,  but  fertilization  does  not  occur  until  the  cocoon 
is  slipped  over  the  head  (Fig.  159,  B). 

The  eggs  of  the  earthworm  are  holoblastic,  but  cleavage  is 
unequal.  A  hollow  blastula  is  formed  and  a  gastrula  is  produced 
by  invagination.     The  mesoderm  develops  from  two  of  the 


228 


COLLEGE  ZOOLOGY 


blastula  cells,  called  mesomeres.  These  cells  divide,  forming  two 
mesohlastic  hands  which  later  become  the  epithelial  lining  of 
the  ccelom.  The  embryo  escapes  from  the  cocoon  as  a  small 
worm  in  about  two  or  three  weeks. 

Behavior.  —  External  Stimuli.  —  The  external  stimuli  that 
have  been  most  frequently  employed  in  studying  the  behavior 
of  earthworms  are  those  dealing  with  thig- 
motropism,  chemotropism,  and  phototropism. 

Thigmotropism,  —  Mechanical  stimula- 
tion, if  continuous  and  not  too  strong,  calls 
forth  a  positive  reaction ;    the  worms  live 


Fig.  159.  — A,  the  anterior  segments  of  two  copulating  earthworms.  Slime 
tubes  encircle  the  pair  from  the  8th  to  the  33d  segment.  B,  cocoon,  freshly 
deposited,  of  an  earthworm,  surrounded  by  one-half  of  a  slime  tube.  (After 
Foot,  in  Journ.  Morph.) 


where  their  bodies  come  in  contact  with  solid  objects;  they 
apparently  lil^  to  feel  the  walls  of  their  burrows  against  their 
bodies,  or,  when  outside  of  their  burrows,  to  lie  or  crawl  upon  the 
ground.  Reactions  to  sounds  are  not  due  to  the  presence  of 
a  sense  of  hearing,  but  to  the  contact  stimuli  produced  by  vibra- 
tions. Darwin  showed  that  musical  tones  produced  no  response, 
but  that  the  worms  contained  in  a  flower-pot  drew  back  into 
theh*  burrows  immediately  when  a  note  was  struck,  if  the  pot 
were  placed  upon  a  piano,  this  result  being  due  to  vibrations. 

Chemotropism.  —  In  certain  cases  chemotropic  reactions 
result  in  bringing  the  animal  into  regions  of  favorable  food  con- 
ditions, or  turning  it  away  from  unpleasant  substances.  Mois- 
ture, which  is  necessary  for  respiration,  and  consequently  for  the 
life  of  the  earthworm,  causes  a  positive  reaction,  provided  it 


PHYLUM   ANNELIDA  229 

comes  in  contact  with  the  body,  no  positive  reactions  being 
produced  by  chemical  stimulation  from  a  distance.  Negative 
reactions,  on  the  other  hand,  such  as  moving  to  one  side  or  back 
into  the  burrow,  are  produced  even  when  certain  unpleasant 
chemical  agents  are  still  some  distance  from  the  body.  These 
reactions  are  quite  similar  to  those  caused  by  contact  stimuli. 
Darwin  explained  the  preference  of  the  earthworm  for  certain 
kinds  of  food  by  supposing  that  the  discrimination  between 
edible  and  inedible  substance  was  possible  when  in  contact  with 
the  body.  This  would  resemble  the  sense  of  taste  as  present  in 
the  higher  animals. 

Phototropism.  —  No  definite  visual  organs  have  been  dis- 
covered in  earthworms,  but  nevertheless  these  animals  are  very 
sensitive  to  light,  as  is  proved  by  the  fact  that  a  sudden  illumina- 
tion at  night  will  often  cause  them  to  "  dash  like  a  rabbit  "  into 
their  burrows.  One  investigator  claims  to  have  found  cells  in 
the  ectoderm,  especially  in  the  prostomium  and  posterior  end, 
which  act  as  visual  organs.  The  entire  surface  of  the  body, 
however,  is  sensitive  to  light,  although  the  anterior  region  is 
more  sensitive  than  the  tail,  and  the  middle  less  than  either  of 
the  others.  Very  slight  differences  in  the  intensity  of  the  light 
are  distinguished,  since,  if  a  choice  of  two  illuminated  regions 
is  given,  that  more  faintly  lighted  is,  in  the  majority  of  cases, 
selected.  A  positive  reaction  to  faint  light  has  been  demon- 
strated for  the  manure  worm,  Allolobophora  fcetida.  This 
positive  phototropism  to  faint  light  may  account  for  the  emer- 
gence of  the  worms  from  their  burrows  at  night. 

Physiological  State.  —  From  the  foregoing  account  it 
might  be  inferred  that  only  external  stimuli  are  factors  in  the 
behavior  of  the  earthworm.  This,  however,  is  not  the  case, 
since  the  physiological  condition,  which  depends  largely  upon 
previous  stimulation,  determines  the  character  of  the  response. 
Different  physiological  states  may  be  recognized,  ranging  from 
a  state  of  rest  in  which  slight  stimuli  are  not  effective,  to  a  state 
of    great   excitement   caused    by   long-continued    and    intense 


230 


COLLEGE  ZOOLOGY 


stimulation,  in  which   condition   slight   stimuli   cause   violent 
responses. 

Regeneration  and  Grafting.  —  Earthworms  have  considerable 
powers  of  regeneration  and  grafting  (p.  117).  Some  of  the  results 
of  experiments  along  this  line  are  shown  in  Figure  160.  A 
posterior  piece  may  regenerate  a  head  of  five  segments  (A)  or 
in  certain  cases  a  tail  (B).  Such  a  double- tailed  worm  slowly 
starves  to  death.     An  anterior  piece  regenerates  a  tail   (C). 

Three  pieces  from  several  worms  may 
be  united  so  as  to  make  a  long 
worm    (D) ;    two   pieces    may    fuse, 


Fig.  160.  —  Regeneration  and  grafting  in  the  earthworm.  A,  head  end  of 
five  segments  regenerated  from  the  posterior  piece  of  a  worm.  B,  tail  re- 
generated from  the  posterior  piece  of  a  worm.  C,  tail  regenerated  from  an 
anterior  piece  of  a  worm.  D,  union  of  three  pieces  to  make  a  long  worm. 
E,  union  of  two  pieces  to  make  a  double-tailed  worm.  F,  anterior  and  pos- 
terior pieces  united  to  make  a  short  worm.  The  dotted  portion  represents 
regenerated  material.     (From  Morgan.) 


forming  a  worm  with  two  tails  (E) ;  and  an  anterior  piece  may 
be  united  with  a  posterior  piece  to  make  a  short  worm  (F). 
In  all  these  experiments  the  parts  were  held  together  by  threads 
until  they  became  united. 

Econoniic  Importance.  —  Charles  Darwin  in  his  book  on  the 
Formation  of  Vegetable  Mold  through  the  Action  of  Worms  has 
shown  by  careful  observations  extending  over  a  period  of  forty 
years  how  great  is  the  economic  importance  of  earthworms. 
One  acre  of  ground  may  contain  over  fifty  thousand  earthworms. 


PHYLUM   ANNELIDA  23 1 

The  faeces  of  these  worms  are  the  Httle  heaps  of  black  earth, 
called  "  castings  "  which  strew  the  ground,  being  especially 
noticeable  early  in  the  morning.  Darwin  estimated  that  more 
than  eighteen  tons  of  earthy 
castings  may  be  carried  to  the  >^^':^-^^y^^.->''^^'--^-'y''yy 
surface  in  a  single  year  on  one  f^^?^ 
acre  of  ground,  and  in  twenty- 
years  a  layer  three  inches 
thick  would  be  transferred 
from  the  subsoil  to  the  sur- 
face.    By  this  means  objects 

are  covered  up  in  the  course  ^'  I? 

of     a    few    years.       Darwin     i       ^  r"^  "^ 


^ 


speaks  of  a  stony  field  which 


pO^  "^.i^. 


V, 


was  so  changed  that  "  after    |  (J[^  ^^ 

thirty  years   (187 1)    a    horse     [  ■ 


could    gallop     over    the     com-  Fig.  lOi.  — Section  through  the  upper 

pact  turf  from  one  end  of  the  stratum  of  a  field  showing  the  work  of 

earthworms.       A    and     B,    arable    soil 

held    to    the    other,    and    not  thrown   up   by   earthworms.      C,    marl 

strike   a   single    stone  with   its  ^^^  cinders  buried  by  worm   castings. 

1-              /-T"         /r    \  ^'  subsoil  not  disturbed  by  the  earth- 

Shoes       (tig.   161).  worms.     (From  Schmeil.) 

The  continuous  honeycomb- 
ing of  the  soil  by  earthworms  makes  the  land  more  porous  and 
insures   the   better    penetration    of    air   and    moisture.      The 
thorough  working  over  of  the  surface  layers  of  earth  also  helps 
to  make  the  soil  more  fertile. 

2.   Classification  of  Annelids 

Definition.  —  Annelids  are  segmented  worms,  the  body 
consisting  of  a  linear  series  of  more  or  less  similar  parts.  Many 
of  the  internal  organs  are  segmentally  arranged,  notably  the 
blood-vessels,  excretory  organs,  and  nervous  system.  A  large 
perivisceral  coelom  is  usually  present,  and  in  some  cases  a  tro- 
chophore  stage  (Fig.  162)  appears  in  development.  Setae  are 
characteristics  of  the  majority. 


232 


COLLEGE  ZOOLOGY 


The  classes  of  annelids  are  as  follows:  — 

(i)  Class  Archiannelida.  —  Marine  worms  without  setae  or 
parapodia.  There  is  only  one  family,  including  two  genera. 
Example:    Polygordius  (Fig.  162). 

(2)  Class  Chaetopoda.  —  Marine,  fresh-water,  or  terrestrial 
worms  with  setae  and  a  perivisceral  coelom ;  often  divided  by 
septa.     Examples:  Lumbricus  (Fig.  154),  Nereis  (Fig.  163). 

(3)  Class  Hirudinea.  —  Marine,  fresh-water,  or  terrestrial 
worms  without  setae  or  parapodia.  Anterior  and  posterior 
suckers  are  present.  Examples:  Hirudo  (Fig.  169),  Clepsine 
(Fig.  171). 

3.   Class  I.    Archiannelida 

A  single  family,  Polygordiid^,  belongs  to  this  class;  it 
includes  two  genera,  Polygordius  (Fig.  162,  A)  and  Protodrilus. 

■e  \  P-cc.  ^^ct 

k 


Fig.  162.  —  Polygordius  appendiculatus.  A,  dorsal  view.  an,  anus; 
ct.,  cephalic  tentacles;  A,  head.  B,  trochosphere  larva,  an,  anus;  e,  eye-spot; 
m.,  mouth.  C  and  D,  stages  in  development  of  trochosphere  into  the  worm. 
Pnp,  pronephridium.     (From  Bourne,  after  Fraipont.) 


PHYLUM   ANNELIDA 


^2>2> 


Polygordius  is  a  marine  worm  living  in  the  sand.  It  is  about 
an  inch  and  one  half  long,  and  only  indistinctly  segmented 
externally.  The  prostomium  (Fig.  162,  h)  bears  a  pair  of  ten- 
tacles (ct.).  The  mouth  opening  is  in  the  ventral  part  of  the  first 
segment,  and  the  anal  opening  {an}  in  the  last  segment.  A  pair 
of  ciliated  pits,  one  on  either  side  of  the  prostomium,  •probably 
serve  as  sense-organs. 

Internally  Polygordius  resembles  the  earthworm,  but  in  some 
respects  is  more  primitive.  The  coelom  is 
divided  into  compartments  by  septa.  The 
internal  organs  are  repeated  so  that  almost 
every  segment  possesses  coclomic  cavities, 
longitudinal  muscles,  a  pair  of  nephridia,  a 
pair  of  gonads,  a  section  of  the  alimentary 
canal,  and  part  of  the  ventral  nerve-cord. 
The  development  of  Polygordius  includes  a 
trochophore  stage.  As  shown  in  Figure  162,  B, 
the  trochophore  larva  at  first  resembles  a  top 
with  cilia  around  the  edge,  an  eye-spot  (e),  and 
a  digestive  tract  with  both  mouth  {m)  and 
anal  {an)  openings.  This  larva  resembles  the 
Pilidium  larva  of  the  Nemertinea  (Fig.  118) 
and  certain  adult  rotifers  (Figs.  122-123). 
The  adult  develops  from  the  larva  by  the 
growth  and  elongation  of  the  anal  end  as 
shown  in  Figure  162,  B,  C.  This  elongation 
becomes  segmented  (D)  and  by  continued 
growth  transforms  into  the  adult  (A). 


4.   Class  II.     Ch^topoda 

The  Ch^topoda  are  annelids  which  possess 
conspicuous  setae.  Two  subclasses  are  recog- 
nized: (i)  the  PoLYCH^TA,  like  Nereis  (Fig. 
163),  with  many  setae  situated  on  paired  fleshy 
outgrowths,  the  parapodia  (Fig.  164,  para),  and 


234 


COLLEGE  ZOOLOGY 


tc^ 


perid.hrd 


v&it.vess 


Fig.  164. — Anatonn-  ui  7-5.  vess,  dor- 

sal vessel;  gl,  oesophageal  Kiaiuis;  iyit,  intestine; 
ne.co,  nerve-cord;  neph,  nephridia;  ces,  oesoph- 
agus; palp,  palp;  para,  parapodia;  perist,  peri- 
stome ;  perist.tent,  peristomial  tentacle ;  ph, 
pharynx  with  its  jaws  ;  praest,  prostomium  ; 
tent,  prostomial  tentacles ;  vent.vess,  ventral 
vessels.     (From  Parker  and  Haswell.) 


the  sexes  usually  separ- 
ate; and  (2)  the  Oligo- 
CILETA,  like  the  earth- 
worm, with  a  lesser 
number  of  sessile  setae 
projecting  out  from  the 
body- wall ;  hermaphro- 
ditic. 

Subclass  I.    Polych(Bta 

Nereis.  —  Nereis  (Fig. 
163),  the  sand  or  clam 
worm,  is  a  common 
annelid  living  in  burrows 
in  the  sand  or  mud  of  the 
sea-shore  at  tide  level. 
The  burrows  are  some- 
times two  feet  deep  and 
are  kept  from  collapsing 
by  a  lining  of  mucus 
which  holds  together  the 
grains  of  sand.  By  day 
the  sandworm  rests  in 
its  burrow,  but  at  night 
it  extends  its  body  in 
search  of  food,  or  may 
leave  the  burrow  en- 
tirely. 

A  comparison  of  the 
figures  of  Nereis  (Figs. 
163-165)  with  those  of 
the  earthworm  (Figs. 
153-154)  shows  that 
these  two  animals  have 
much   in  common,  but 


PHYLUM   ANNELIDA 


235 


nevertheless  many  differences.  Both  are  segmented  externally 
and  internally,  but  Nereis  possesses  parapodia  (Fig.  164,  para), 
a  pair  of  chitinous  jaws,  a  pair  of  tentacles  {tent),  and  two  pairs 
of  eyes  on  the  prostomium  (praest),  a  pair  of  palpi  (palp), 
and  four  pairs  of  tentacles  on  the  peristome  (perist.tent) . 

The  parapodia  (Fig.  165) 
are  primarily  used  as  loco- 
motor organs,  but  the  lobes 
(DP  and  VF)  are  supplied 
with  numerous  blood- 
vessels and  serve  also  as 
respiratory  organs  or  gills. 
Each  parapodium  bears 
jointed  locomotor  setce,  and 
is   moved  by  muscles   at- 


huud 


Fig.  165.  —  Parapodium  of 
Nereis  Ac,  aciculum;  Be,  ven- 
tral cirrus;  DP,  notopodium ; 
Re,  dorsal  cirrus;  V P,  neuro- 
podium,  with  bundles  of  setae. 
(From  Sedgwick,  after  Quatre- 
fages.) 


Fig.  166.— APoly- 
chaet,  Autolytus, 
which  reproduces  by 
buds,  bud,  head  of 
the  budded  indi- 
vidual. (From 
Davenport,  after 
Agassiz.) 


Fig.  167.- — Am- 
phitrite  johnstoni. 
g,  gills ;  /,  prosto- 
mial  tentacles. 
(From  Sedgwick, 
after  Cunningham 
and  Ramage.) 


tached  to  a  sort  of  internal  skeleton  consisting  of  two  buried 
bristles  called  acicida  {Ac). 

The  sense  organs  of  Nereis  are  more  highly  developed  than 
those  of  the  earthworm.  The  tentacles  (Fig.  164,  perist.tent) 
are  organs  of  touch,  the  palpi  {palp)  are  probably  organs  of 
taste,  and  the  eyes,  organs  of  sight. 


236 


COLLEGE  ZOOLOGY 


The  two  principal  groups  of  the  Polych^ta  are  the  Phane- 
ROCEPHALA  and  Crypto  CEPHAL A. 

Order  i.  Phanerocephala. — Polych^ta  with  most  of  the 
segments  similar,  a  distinct  head  (prostomium)  and  a  protrusible 
pharynx  usually  provided  with  chitinous  jaws.  Examples: 
Nereis  (Fig.  163),  Aphrodite,  Autolytus  (Fig.  166). 

Order  2.  Cryptocephala.  —  Polychaeta  with  head  (prosto- 
mium) usually  small  and  indistinct;  segments  differentiated, 
forming  two  or  more  regions,  the  thorax  and  abdomen,  and 
palpi  often  divided  into  a  crown  of  gills.  Examples:  Amphi- 
trite  (Fig.  167),  Spirorbis,  Terebella,  Sabella. 


Subclass  2.   OligochcBta 

The  earthworm  illustrates  the  chief  characteristics  of  this 
subclass.     There  are  usually  only  a  few  setae,  and  no  parapodia 

nor  tentacles.  The  sexes  are  united, 
i.e.  hermaphroditic.  Most  of  the 
Oligoch^ta  are  either  terrestrial 
or  live  in  fresh  water.  Two  orders 
are  recognized:  (i)  the  Microdrili, 
and  (2)  the  Macrodrili. 

Order  i.      Microdrili  (Limicola). 

—  These  are  mostly  small  fresh- 
water animals.  Examples:  Tubifex, 
Dero,  Nats  (Fig.  168).  Many  of 
them  reproduce  by  transverse  fission 
as  well  as  sexually. 

Order  2.    Macrodrili.    (Terricola). 

—  This  order  contains  the  terrestrial 
Examples:   Lumbricus  (Fig.  154),  Allolobophora, 


Fig.  168. — Nats,  a,  mouth; 
b,  anus ;  c,  intestine.  (From 
Davenport,   after  Leunis.) 


Oligoch^ta 
Diplocardia. 


5.   Class  III.    Hirudinea 


The  animals  included  in  this  class  are  commonly  called  leeches 
(Fig.    169).     They  are  usually  flattened  dorso-ventrally,  but 


PHYLUM   ANNELIDA 


237 


differ  externally  from  the  flatworms  (Platyhelminthes,  Chap. 
VII)  in  being  distinctly  segmented.  The  external  segmenta- 
tion, however,  does  not  correspond  exactly  to  the  internal  seg- 
mentation, since  there  are  a  variable  number  of  external  grooves 
(from  two  to  fourteen)  to  everf  real 
segment,  e.g.  usually  five  in  the  me- 
dicinal leech,  Hirudo  (Fig.  169),  and 
its  allies,  and  three  in  Clepsine. 
Anatomical  features  which  distinguish 
the  HiRUDiNEA  from  the  Archian- 
NELiDA  and  CH.ETOPODA  are  (i)  the 
presence  of  a  definite  number  of  seg- 
ments (thirty- three),  (2)  two  suckers 
(Fig.  169,  I,  2),  one  formed  around 
the  mouth  and  the  other  at  the  pos- 
terior end,  and  (3)  the  absence  of 
setae  (except  in  one  genus).  They 
are  hermaphrodites. 

Hirudo  medicinalis,  the  medicinal 
leech  (Fig.  169),  is  usually  selected  as 
an  example  of  the  class.  It  is  about 
four  inches  long,  but  is  capable  of 
great  contractions  and  elongation. 
The  suckers  are  used  as  organs  of 
attachment,  and  during  locomotion 
are  alternately  fastened  to  and  re- 
leased from  the  substratum,  the  animal      ^^^-  169.  —  A  leech,  Hirudo 

.  .  medicinalis.    7,  mouth;  2,  pos- 

loopmg  along  like  a  meaSUrmg-WOrm.    terior  sucker;  3,  sensory  papil- 

Leeches  are  also  able  to  swim  through  !*•    (^rom  Shipley  and  Mac- 

1  ,  1    ,      .  Bride.) 

the  water  by  undulatmg  movements. 

The  alimentary  trad  (Fig.  170,  j-7)  is  fitted  for  the  digestion 
of  the  blood  of  vertebrates,  which  forms  the  principal  food  of 
some  leeches.  The  mouth  lies  in  the  anterior  sucker  (Fig.  169,  i) 
and  is  provided  with  three  jaws  armed  with  chitinous  teeth  for 
biting.     The  blood  flow  caused  by  the  bite  of  a  leech  is  difficult 


ten  I     in 

men'    ttv 

[fill  ■III 


(irii     in 


»!»»     lit 

lU'    "J 


22,^ 


COLLEGE   ZOOLOGY 


..V-i2 


to  stop,  since  a  secretion  from  glands  opening  near  the  jaws  tends 

to  prevent  coagulation.  Blood  is 
sucked  up  by  the  dilation  of  the  mus- 
cular pharynx  (Fig.  170,  2).  The  short 
cesophagus  leads  from  the  pharynx 
into  the  crop,  which  has  eleven  pairs 
of  lateral  branches  (j,  4).  Here  the 
blood  is  stored  until  digested  in  the 
small  globular  stomach  (5).  A  leech 
is  able  to  ingest  three  times  its  own 
weight  in  blood,  and,  since  it  may 
take  as  long  as  nine  months  to  digest 
this  amount,  meals  are  few  and  far 
between.  The  intestine  (6)  leads 
directly  to  the  anus  (7). 

The  absorbed  food  passes  into  the 
blood-vessels  (Fig.  170,  11)  and  the 
coelomic  cavities,  and  is  carried  to  all 
parts  of  the  body.  The  coelom  is 
usually  small  because  of  the  develop- 
ment of  a  peculiar  kind  of  connective 
tissue  known  as  botryoidal  tissue.  The 
spaces  in  the  body  which  are  not  filled 
up  by  this  tissue  are  called  sinuses, 
and  in  many  species  contain  a  fluid 
very  much  like  true  blood. 

Respiration  is  carried  on  at  the 
surface  of  the  body,  oxygen  being 
taken  into  and  carbon  dioxide  given 
off  by  many  blood  capillaries  in  the 

Fig.  170. — View  of  the  internal  organs  of  the  leech,  Hirudo  medicinalis. 
I,  head  with  eye-spots;  2,  muscular  pharynx;  5,  ist  diverticulum  of  crop; 
4,  nth  diverticulum  of  crop;  5,  stomach;  6,  rectum;  7,  anus;  8,  cerebral 
ganglia;  q,  ventral  nerve-cord;  10,  nephridium;  11,  lateral  blood-vessel; 
12,  testis;  13,  vas  deferens;  14,  prostate  gland;  75,  penis;  16,  ovary;  i/,  uterus. 
(From  Shipley  and  MacBride.) 


PHYLUM   ANNELIDA  239 

skin.  Waste  products  are  extracted  from  the  blood  and  coelomic 
fluid  by  seventeen  pairs  of  nephridia  (Fig.  170,  10)  which  re- 
semble those  of  the  earthworm  (Fig. 
153,  neph)j  but  frequently  lack  the 
internal  opening.  *" 

Leeches  are  hermaphroditic,  but  the 
eggs  of  one  animal  are  fertilized  by 
spermatozoa  from  another  leech.  The 
spermatozoa  arise  in  the  nine  pairs 
of  segmentally  arranged  testes  (Fig, 
170,  12);  they  pass  into  the  vas 
deferens  {13),  then  into  a  convoluted 
tube  called  the  epididymus  {14),  w^here 
they  are  fastened  into  bundles  called 
spermatophores,  and  are  finally  de- 
posited within  the  body  of  another 
leech  by  means  of  the  muscular  penis. 
The  eggs  arise  in  the  ovaries  of  which 
there  is  a  single  pair  {16) ;  they  pass 
into  the  oviducts,  then  into  the 
uterus  (ly),  and  finally  out  through 
the  genital  pore  ventrally  situated  in 
segment  XI.  Copulation  and  the 
formation  of  a  cocoon  are  similar  to 

.,  •        ^1  ^1  Fig.    171. — Two    leeches. 

these    processes    m    the    earthworm    a,  Pontobdeiia.    B,  Ckpsine. 

(p.   226).  (From   Parker  and    Haswell. 

-.--  Ill  •  *     1  !•  A,    after    Bourne;     B,    after 

Many  leeches  nave  jaws  resemblmg    Cuvier.) 
those  of  Hirudo,  for  example  Hcemopis 

and  Macrobdella,  but  others  have  a  slender  protrusible  proboscis 
in  place  of  jaws.  Clepsine  (Fig.  171)  belongs  to  the  latter 
type;  it  feeds  chiefly  on  fish  and  snails.  I chthyohdella  and 
Pontobdeiia  (Fig.  171)  are  marine  jawless  leeches  which  are 
parasitic  on  fish. 


240  COLLEGE  ZOOLOGY 

6.  Annelids  in  General 

Three  morphological  characteristics  of  the  Annelida  are  espe- 
cially worthy  of  notice:  (i)  metamerism,  (2)  the  coelom,  and 
(3)  the  trochophore  stage  in  development. 

Metamerism.  —  The  segmentation  of  the  body  as  exhibited 
in  annelids  is  called  metamerism,  and  is  here  encountered  for  the 
first  time.  This  type  of  structure  is  of  considerable  interest,  since 
the  most  successful  groups  in  the  animal  kingdom,  the  Arthro- 
PODA  and  Vertebrata,  have  their  parts  metamerically  arranged. 
How  this  condition  has  been  brought  about  is  still  doubtful,  but 
many  theories  have  been  proposed  to  account  for  it.  According 
to  one  view  the  body  of  a  metameric  animal  has  evolved  from 
that  of  a  non-segmented  animal  by  transverse  fission.  The  in- 
dividuals thus  produced  remained  united  end  to  end  and  gradu- 
ally became  integrated  both  morphologically  and  physiologi- 
cally so  that  their  individualities  were  united  into  one  complex 
individuality.  Some  zoologists  maintain  that  the  segmental 
arrangement  of  organs  such  as  nephridia,  blood-vessels,  and  re- 
productive organs  has  been  caused  by  the  division  of  a  single 
ancestral  organ,  and  not  by  the  formation  of  new  organs  as  the 
fission  theory  demands. 

True  metamerism,  as  exhibited  by  annelids,  should  not  be 
confused  with  the  pseudometamerism  of  the  tapeworms  (p.  163, 
Fig.  107).  The  proglottides  of  the  tapeworms  are  individuals 
budded  off  from  the  posterior  end  and  differing  from  one  another 
only  in  the  degree  of  development.  The  tapeworm  may  be 
considered  a  row  of  incomplete  individuals. 

The  Coelom.  —  The  coelom  has  already  been  defined  (p.  89) 
as  a  cavity  in  the  mesoderm  lined  by  an  epithelium;  into 
•it  the  excretory  organs  open,  and  from  its  walls  the  reproductive 
cells  originate.  The  development  of  the  coelom  is  described 
on  page  89. 

The  importance  of  the  coelom  should  be  clearly  understood, 
since  it  has  played  a  prominent  role  in  the  progressive  develop- 


PHYLUM   ANNELIDA  24I 

ment  of  complexity  of  structure.  The  appearance  of  this  cavity 
between  the  digestive  tract  and  body- wall  brought  about  great 
physiological  changes  and  is  correlated  with  the  origin  of  ne- 
phridia  for  transporting  waste  pr9ducts  out  of  the  body,  and  of 
genital  ducts  for  the  exit  of  eggs  and  spermatozoa.  The  coelom 
also  affected  the  distribution  of  nutritive  substances  within  the 
body,  since  it  contains  a  fluid  which  takes  up  material  absorbed 
by  the  alimentary  canal  and  carries  it  to  the  tissues.  Excretory 
matter  finds  its  way  into  the  ccelomic  fluid  and  thence  out  of 
the  body  through  the  nephridia. 

So  important  is  the  coelom  considered  by  most  zoologists 
that  the  Metazoa  are  frequently  separated  into  two  groups:  (i) 
the  AccELOMATA  without  a  ccelom,  and  (2)  the  Ccelomata  with 
a  coelom.  The  Porifera,  Ccelenterata,  and  Ctenophora 
are  undoubtedly  A  ccelomata.  Likewise  the  Annelida, 
EcHiNODERMATA,  Arthropoda,  Mollusca,  and  Chord  ATA 
are  certainly  Ccelomata.  But  whether  the  Platyhelminthes, 
Nemathelminthes,  and  a  number  of  other  groups  possess  a 
coelom  is  still  uncertain  (see  p.  25). 

The  Trochophore.  —  The  term  trochophore  has  been  applied 
to  the  larval  stages  of  a  number  of  marine  animals.  The  de- 
scription and  figures  of  the  development  of  Polygordius  (p.  233, 
Fig.  162)  are  sufficient  to  indicate  the  peculiarities  of  this  larva. 
Many  other  marine  annelids  pass  through  a  trochophore  stage 
during  their  life-history;  those  that  do  not  are  supposed  to  have 
lost  this  step  during  the  course  of  evolution. 

Since  a  trochophore  also  appe^,rs  in  the  development  of  ani- 
mals belonging  to  other  phyla,  for  example,  Mollusca  and 
Bryozoa,  and  resembles  very  closely  certain  Rotifera,  the  con- 
clusion has  been  reached  by  some  embryologists  that  these 
groups  of  animals  are  all  descended  from  a  common  hypo- 
thetical ancestor,  the  trochozoon.  Strong  arguments  have 
been  advanced  both  for  and  against  this  theory. 


CHAPTER    XII 


PHYLUM   MOLLUSCA 


The  Phylum  Mollusca  (Lat.  mollis,  soft)  includes  the  snails, 
slugs,  clams,  oysters,  octopods,  and  nautili.   They  are  primitively 

bilaterally  symmetrical,  but 
unsegmented,  and  many  of 
them  possess  a  shell  of  cal- 
cium carbonate.  Mussels 
(Fig.  1 73), clams,  snails  (Fig. 
180),  and  squids  (Fig.  191) 
do  not  appear  at  first  sight 
to  have  much  in  common, 
but  a  closer  examination 
reveals  several  structures 
possessed  by  all.  One  of 
these  is  an  organ  called  the 
foot,  which  in  the  snail  (Fig. 
172,  I,  4)  is  usually  used 
for  creeping  over  surfaces, 
in  the  clam  (II,  4)  gener- 
ally for  plowing  through  the 
mud,  and  in  the  squid  (III,  4) 
for  seizing  prey.      In   each 


Fig.   172.  —  Diagrams  of  three  types  of 
moUusks,  —  I,  a  Prosobranch  Gastropod. 
II   a  Lamellibranch,  and  III   a  Cephalo-     ^^^^^    -^   ^   ^    ^^^    ^^^^^^    ^j^^ 
pod,  to  show  the  form  of  the  foot   and  ^ 

its  regions  and  the  relations  of  the  vis- 
ceral hump  to  the  antero-posterior  and 
dorso-ventral  axes.  A,  anterior  surface; 
D,  dorsal  surface;  P,  posterior  surface; 
V,  ventral  surface;  /,  mouth;  2,  anus; 
5,  mantle  cavity;  4,  foot.  (From  Shipley 
and  MacBride,  after  Lankester.) 

242 


mantle  cavity  (Fig.  172,  j) 
between  the  main  body  and 
an  enclosing  envelope,  the 
mantle.  The  anus  (2)  opens 
into  the  mantle  cavity. 


PHYLUM   MOLLUSCA  243 

The  moUusks  are  divided  into  five  classes  according  to  their 
symmetry  and  the  characters  of  the  foot,  shell,  mantle,  gills,  and 
nervous  system. 

Definition.  —  Phylum  Mollusca.  Clams,  Snails,  Squids, 
OcTOPi.  Triploblastic,  bilaterally  symmetrical  animals;  anus 
and  coelom  present;  no  segmentation;  shell  usually  present; 
the  characteristic  organ  is  a  ventral  muscular  foot. 

Class  I.  Amphineura  (Gr.  amphi,  on  both  sides;  neuron, 
a  nerve),  the  chitones  (Fig.  179),  with  bilateral  symmetry,  often 
a  shell  of  eight  transverse  calcareous  plates,  and  many  pairs  of 
gill  filaments; 

.  Class  II.  Gastropoda  (Gr.  gaster,  the  belly;  pous,  a  foot), 
the  snails  (Fig.  180),  slugs  (Fig.  184),  whelks,  etc.,  with  a 
symmetry  and  usually  a  spirally  coiled  shell; 

Class  III.  Scaphopoda  (Gr.  skaphe,  a  boot;  pous,  a  foot),  the 
elephants'-tusk  shells  (Fig.  188),  with  tubular  shell  and  mantle; 

Class  IV.  Pelecypoda  (Gr.  pelekos,  hatchet;  pous,  a  foot), 
the  clams,  mussels  (Fig.  174),  oysters,  and  scallops,  usually  with 
bilateral  symmetry,  a  shell  of  two  valves,  and  a  mantle  of  two 
lobes; 

Class  V.  Cephalopoda  (Gr.  kephale,  head;  pous,  a  foot), 
the  squids  (Fig.  191),  cuttlefishes,  octopods  (Fig.  196),  and 
nautili  (Fig.  194),  with  bilateral  symmetry,  a  foot  divided  into 
arms  provided  with  suckers,  and  a  well-developed  nervous  system 
concentrated  in  the  head. 

I.   The  Pearly  Fresh-water  Mussel  —  Anodonta  and 

THE   UnIONES 

The  fresh-water  mussel  is  a  mollusk  belonging,  together  with 
the  oyster,  the  long-neck  clam,  the  scallop,  and  other  similar 
animals,  to  the  class  Pelecypoda.  Mussels  inhabit  the  lakes 
and  streams  of  this  country  wherever  the  water  contains  car- 
bonate of  lime  and  does  not  entirely  evaporate  during  any  part 
of  the  year.  Anodonta  and  the  Uniones  are  similar  except  for 
minor  details. 


244 


COLLEGE  ZOOLOGY 


External  Features.  —  Mussels  usually  lie  almost  entirely 
buried  in  the  muddy  or  sandy  bottom  of  lakes  or  streams.  They 
burrow  and  move  from  place  to  place  by  means  of  the  foot  (Fig. 
173,  g),  which  can  be  extended  .from  the  anterior  end  of  the 
shell.  Water  loaded  with  oxygen  and  food  material  is  drawn 
in  through  a  slit-like  opening  at  the  posterior  end,  called  the 

ventral     siphon    (8), 

8^.^|^^^H^H^^|^^^    2        and    excretory   sub- 

4...  J^^^^^K^^KI^^^^^^  stances    and     faeces 

along  with  deoxy- 
genated  water  are 
carried  out  through 
a  smaller  dorsal 
siphon  (7). 

The  Shell.— The 
shell  consists  of  two 
:^c^^  parts,  called  valves 
(Fig.  173),  which  are 
fastened  together  at 
the  dorsal  surface  by 
an  elastic  ligamen- 
tous hinge.  In  Unio 
the  valves  articulate 
with  each  other  by 
means  of  projections 
called  teeth,  but 
these  are  almost  entirely  atrophied  in  Anodonta.  A  number  of 
concentric  ridges  appear  on  the  outside  of  each  valve;  these  are 
called  lines  of  growth  (Fig.  173,  10),  and,  as  the  name  implies,  rep- 
resent the  intervals  of  rest  between  successive  periods  of  growth. 
The  small  area  situated  dorsally  toward  the  anterior  end  is 
called  the  umbo  (6) ;  this  is  the  part  of  the  shell  with  which  the 
animal  was  provided  at  the  beginning  of  its  adult  stage.  The 
umbo  is  usually  eroded  by  the  carbonic  acid  in  the  water. 
The  structure  of  the  shell  is  easily  determined.     There  are  three 


Fig.  173.  —  External  features  of  a  clam,  Anodonta 
mutabilis.  Behind  is  the  inner  face  of  an  empty 
shell.  /,  points  of  insertion  of  anterior  protractor 
(above)  and  retractor  muscles  (below)  of  the  shell; 
2,  of  anterior  adductor  muscle;  j,  of  posterior  pro- 
tractor of  the  shell;  4,  of  posterior  adductor  muscle; 

5,  lines  formed  by  successive  attachment  of  mantle; 

6,  umbo;  7,  dorsal  siphon;  8,  ventral  siphon;  q,  foot 
protruded;  10,  lines  of  growth.  (From  Shipley  and 
MacBride.) 


PHYLUM   MOLLUSCA  245 

layers:  (i)  an  outer  thin,  homy  layer,  the  pericrstracum,  which 
is  secreted  by  the  edge  of  the  mantle, —  it  serves  to  protect  the 
underlying  layers  from  the  carbonic  acid  in  the  water,  and  gives 
the  exterior  of  the  shell  most  of  i^s  Qolor;  (2)  a  middle  portion 
of  crystals  of  carbonate  of  lime,  called  the  prismatic  layer,  which 
is  also  secreted  by  the  edge  of  the  mantle;  and  (3)  an  inner  na- 
creous layer  (mother-of-pearl),  which  is  made  up  of  many  thin 
lamellae  secreted  by  the  entire  surface  of  the  mantle,  and  pro- 
duces in  the  light  an  iridescent  sheen. 

Anatomy     and     Physiology.  —  General     Account.  —  The 
valves  of  the  shell  are  held  together  by  two  large  transverse 


14.  j^ 


16 

Fig.  174.  —  Right  side  of  Anodonia  mutahilis  with  mantle  cut  away  and 
right  gills  folded  back.  i,  mouth ;  2,  anus ;  3,  cerebro-pleural  ganglion ; 
4,  anterior  adductor  muscle;  5,  anterior  protractor  muscle  of  shell;  6,  re- 
tractor muscle;  7,  dorsal  siphon;  8,  inner  labial  palp;  q,  foot;  10,  external 
opening  of  nephridium;  11,  opening  of  genital  duct;  12,  outer  right  gill- 
plate;  13,  inner  right  gill-plate  ;  14,  ventral  siphon;  15,  epibranchial  chamber; 
16,  posterior  protractor  muscle.  (From  Shipley  and  MacBride,  after  Hatschek 
and  Cori.) 

muscles  which  must  be  cut  in  order  to  gain  access  to  the  internal 
organs.  These  muscles  are  situated  one  close  to  either  end  near 
the  dorsal  surface;  they  are  called  anterior  adductors  (Fig.  174, 
4;  Fig.  175,  a.ad)  and  posterior  adductors  (Fig.  175,  p.  ad). 
As  the  shell  grows,  they  migrate  outward  from  a  position  near 
the  umbo,  as  indicated  by  the  faint  lines  in  Figure  173.  When 
these  muscles  are  cut,  or  when  the  animal  dies,  the  shell  gapes 


246  COLLEGE  ZOOLOGY 

open,  the  valves  being  forced  apart  by  the  elasticity  of  the 
ligamentous  dorsal  hinge,  which  is  compressed  when  the  shell  is 
closed. 

The  two  folds  of  the  dorsal  wall  of  the  mussel  which  line 
the  valves  are  called  the  mantle  or  pallium  (Fig.  175,  m). 
The  mantle  flaps  are  attached  to  the  inner  surface  of  the 
shell  along  a  line  shown  at  5  in  Figure  173.  The  space  be- 
tween the  mantle-flaps  containing  the  two  pairs  of  gill  plates 
(Fig.  174,  72,  ij),  the  foot  (p),  and  the  visceral  mass,  is  called 
the  mantle  cavity. 

Digestion.  —  The  food  of  the  mussel  consists  of  organic 
material  carried  into  the  mantle  cavity  with  the  water  which 
flows  through  the  ventral  siphon  (Fig.  173,  8;  Fig.  174,  14). 
The  mouth  (Fig.  174,  i;  Fig.  175,  mth)  lies  between  two  pairs 
of  triangular  flaps,  called  labial  palps  (Fig.  174,  8).  The  cilia 
on  these  palps  drive  the  food  particles  into  the  mouth.  A  short 
oesophagus  (Fig.  175,  gul)  leads  from  the  mouth  to  the  stomach. 
On  either  side  of  the  stomach  is  a  lobe  of  a  glandular  mass  called 
the  digestive  gland  or  liver  (d.gl) ;  a  digestive  fluid  is  secreted  by 
the  liver  and  is  carried  into  the  stomach  by  ducts,  one  for  each 
lobe. 

The  food  is  mostly  digested  and  partly  absorbed  in  the  stomach; 
it  then  passes  into  the  intestine  (Fig.  175,  int),  by  whose  walls  it  is 
chiefly  absorbed.  The  intestine  coils  about  in  the  basal  portion 
of  the  foot,  then  passes  through  the  pericardium  (pc),  runs  over 
the  posterior  adductor  muscle  {p. ad),  and  ends  in  an  anal 
papilla  (a).  The  faeces  pass  out  of  the  anus  and  are  carried 
away  by  the  current  of  water  flowing  through  the  dorsal  siphon 

(Fig.  173,  ?)• 

Circulation.  —  The  circulatory  system  comprises  a  heart, 
blood-vessels,  and  spaces  called  sinuses.  The  heart  (Fig.  175, 
r.au.,  v)  lies  in  the  pericardium  {pc).  It  consists  of  a  ventricle 
(v)  which  surrounds  part  of  the  intestine  (ret),  and  a  pair  of 
auricles  (r.au).  The  ventricle  by  its  contractions  drives  the 
blood  forward  through  the  anterior  aorta  (a.ao)  and  backward 


PHYLUM   MOLLUSCA 


247 


through  the  posterior  aorta  (p.ao).  Part  of  the  blood  passes  into 
the  mantle,  where  it  is  oxygenated,  and  then  returns  directly 
to  the  heart.  The  rest  of  the  blood  circulates  through  numerous 
spaces  in  the  body   and  is  finally  collected   by  a  vessel  called 


rpit, 
yap  rap     ^^^aao 


"    razi 

hi 

jc    1   CLV.ap 

r.ao    ,P« 

J..^ 

x.sph. 


in. spit 


Fig.  175.  — ^  Internal  anatomy  of  Anodonta  cygnea,  dissection  from  the  left 
side,  a,  the  anus ;  a. ad,  anterior  adductor ;  a.ao,  anterior  aorta ;  a.v  ap, 
auriculo-ventricular  aperture ;  bl,  urinary  bladder ;  c.pl.gn,  cerebro-pleural 
ganglion;  d.d,  duct  of,  digestive  gland;  d.gl,  digestive  gland;  d.p.a,  dorsal 
pallial  aperture;  ex.sph,  exhalant  siphon;  fi,  foot;  g.ap,  genital  aperture; 
gon,  gonad;  gul,  gullet;  i.l.j,  interlamellar  junction;  in.sph,  inhalant  siphon; 
int,  intestine ;  kd,  kidney ;  m,  mantle ;  mth,  mouth  ;  p.ao.  posterior  aorta; 
p. ad,  posterior  adductor;  pc,  pericardium;  pd.gn,  pedal  ganglion;  r.ap,  renal 
aperture;  r.au,  right  auricle;  ret,  rectum;  r.p.a,  reno-pericardial  aperture; 
st,  stomach;  ty,  typhlosole;  v,  ventricle;  v.gn,  visceral  ganglion;  w.t,  water- 
tubes.     (From  Parker  and  Haswell.) 


the  vena  cava,  which  lies  just  beneath  the  pericardium.  From 
here  the  blood  passes  into  the  kidneys,  then  into  the  gills,  and 
finally  through  the  auricles  and  into  the  ventricle.  Nutriment 
and  oxygen  are  carried  by  the  blood  to  all  parts  of  the  body, 
and  carbon  dioxide  and  other  waste  products  of  metabolism  are 
transported  to  the  gills  and  kidneys. 


248 


COLLEGE  ZOOLOGY 


Respiration.  —  The  respiratory  organs  of  the  mussel  are  the 
gills  or  hranchicB  or  ctenidia.     A  pair  of  these  hang  down  into 
the  mantle  cavity  on  either  side  of  the 
foot  (Fig.  176). 

Each  gill  is  made  up  of  two  plates 
or  lamellae  (Fig.  177,  il)  which  lie  side 
by  side  and  are  united  at  the  edges 
except  dorsally  (Fig.  176).  The  cavity 
between  the  lamellae  is  divided  into^ 
vertical  water  tubes  by  partitions  called 
interlamellar  junctions  (Fig.  177,  ilj). 
Each  lamella  consists  of  a  large  number 
of  gill  filaments  {it),  each  supported  by 
two  chitinous  rods  (black  spots  in 
Fig.  177,  il),  and  covered  with  cilia. 
Fig.  176.  — Diagrammatic  Openings,  Called  ostia,  lie  between  the 

section  through  Anodonta 
near  posterior  edge  of  foot. 
I,  right  auricle;  2,  epibran- 
chial  chamber;  3,  ventricle; 
4,  vena  cava ;  5,  non- 
glandular    part    of    kidney ; 

6,  glandular  part  of  kidney; 

7,  intestine  in  foot ;  8,  peri- 
cardium; 9,  shell;   10,  liga-  the  gill  filaments; 
ment  of  shell.    (From  Shiplev    .-,  ^  .t  ;•   7      7        -l       /t?*  -/c     ^\ . 

and  MacBride,  after  Howes.")  the  epihranchial  chamber  (Fig.  176,  2), 
from  here  it  enters  the  dorsal  mantle 
cavity  and  passes  out  through  the  dorsal  siphon  (Fig.  i']S,ex.  sph). 
The  blood  which  circulates  through  the  gills  discharges  carbon 
dioxide  into  the  water  and  takes  oxygen  from  it.  Respiration 
also  takes  place  through  the  surface  of  the  mantle, 

Excretion.  —  The  organs  of  excretion  are  two  U-shaped 
kidneys  or  nephridia  lying  just  beneath  the  pericardium,  one  on 
either  side  of  the  vena  cava  (Fig.  175,  kd).  Each  kidney  con- 
sists of  a  ventral  glandular  portion  (kd)  into  which  the  pericar- 
dium opens  (r.p.a)  by  a  ciliated  slit  and  a  dorsal  thin-walled 
bladder  (bl)  which  opens  to  the  exterior  through  the  renal  aperture 
(r.ap) .    Some  excretory  matter  is  probably  driven  into  the  kidney 


gill  filaments,  and  blood-vessels  (v)  are 
present  in  the  interlamellar  junctions 
and  filaments. 

Water  is  drawn  through  the  ostia  into 
the  water-tubes  by  the  cilia  which  cover 
it  flows  dorsally  into 


PHYLUM  MOLLUSCA 


249 


from  the  pericardium  by  cilia,  and  other  excretory  matter  is 
taken  from  the  blood  by  the  glandular  portion  {kd).  These 
waste  products  of  metabolism  are  carried  out  of  the  body  through 
the  dorsal  siphon  (ex.sph). 

Nervous  System.  —  There  are  t)nly  a  few  ganglia  in  the  body 
of  the  mussel.  On  each  side  of  the  oesophagus  is  a  so-called 
cerebro pleural  ganglion  (Fig. 
175,  c.pl.gn),  connected 
with  its  fellow  by  a  nerve 
called  the  cerebral  commis- 
sure  which  passes  above  the 
oesophagus.  From  each 
cerebropleural  ganglion  a 
nerve-cord  passes  ventrally, 
ending  in  a  pedal  ganglion 
(pd.gn)  in  the  foot.  The 
two  pedal  ganglia  are  closely 
joined  together.  Each  cere- 
bropleural    ganglion  -  also 

gives  off  a  cerebrovisceral  connective  (dotted  in  Fig.  175)  which 
may  be  enclosed  by  the  kidneys  and  leads  to  a  visceral 
ganglion  (v.gn). 

Sensory  Organs.  —  Fresh-water  mussels  are  not  well  pro- 
vided with  sensory  organs.  A  small  vesicle,  the  statocyst,  con- 
taining a  calcareous  concretion,  the  statolith,  lies  a  short  way 
behind  the  pedal  ganglia.  It  is  an  organ  of  equilibrium.  A 
thick  patch  of  yellow  epithelial  cells  covers  each  visceral  ganglion 
and  is  known  as  an  osphradium.  The  functions  of  the  osphradia 
are  not  certain.  They  probably  test  the  water  which  enters  the 
mantle  cavity.  The  edges  of  the  mantle  are  provided  with 
sensory  cells;  these  are  especially  abundant  on  the  ventral  siphon 
(Fig.  175,  in.sph),  and  are  probably  sensitive  to  contact  and 
light. 

Reproduction.  —  Mussels  are  usually  either  male  or  female; 
a  few  are  hermaphroditic.     The  reproductive  organs  are  situated 


Fig.  177.  — Transverse  section  of  por- 
tion of  an  outer  gill-plate  of  Anodonta. 
il,  inner  lamella;  il',  outer  lamella; 
ilj,  interlamellar  junctions;  v,  large  ver- 
tical vessels.  (From  the  Cambridge 
Natural  History,  after  Peck.) 


250 


COLLEGE   ZOOLOGY 


in  the  foot  (Fig.  175,  gon).  They  are  paired  bunches  of  tubes 
and  open  (g.ap)  just  in  front  of  the  renal  aperture  (r.ap)  on 
each  side.  The  spermatozoa  are  carried  out  through  the  dorsal 
siphon  of  the  male  and  in  through  the  ventral  siphon  of  the 
female.  The  eggs  pass  out  of  the  genital  aperture  and  come  to 
lie  in  various  parts  of  the  gills  according  to  the  species.  The 
spermatozoa  enter  the  gill  of  the  female  with  the  water  and 

fertilize  the  eggs.  That  por- 
tion of  the  gill  in  which  the 
eggs  develop  is  termed  the 
marsupium. 

The  eggs  undergo  complete 
but  unequal  segmentation. 
Blastula  and  gastrula  stages 
are  passed  through,  and  then 
a  peculiar  larva  known  as  a 
glochidium  is  produced  (Fig. 
178).  The  glochidium  has  a 
shell  {sh)  consisting  of  two 
valves  which  are  hooked  in 
some  species;  these  may  be  closed  by  a  muscle  {ad)  when  a 
proper  stimulus  is  applied.  A  long,  sticky  thread  called  the 
byssus  (by)  extends  out  from  the  center  of  the  larva,  and 
bunches  of  setcB  (s)  are  also  present. 

In  Anodonta  the  eggs  are  fertilized  usually  in  August,  and  the 
glochidia  which  develop  from  them  remain  in  the  gills  of  the 
mother  all  winter.  In  the  following  spring  they  are  discharged, 
and,  if  they  chance  to  come  in  contact  with  the  external  parts 
of  a  fish,  this  contact  stimulus  causes  them  to  seize  hold  of  it  by 
closing  the  valves  of  their  shell.  The  glochidium  probably 
chemically  stimulates  the  skin  of  the  fish  to  grow  around  it, 
forming  the  well-known  "worms"  or  ''blackheads."  While 
thus  embedded  the  glochidium  receives  nourishment  from  the  fish 
and  undergoes  a  stage  of  development  (metamorphosis),  during 
which  the  foot,  muscles,  and  other  parte  of  the  adult  are  formed. 


at/ 

Fig.  178.  —  The  glochidium  stage 
in  the  development  of  Anodonta. 
ad,  anterior  adductor  muscle ;  by,  bys- 
sus ;  s,  setae ;  sh,  shell.  (From  Lan- 
kester,  after  Balfour.) 


PHYLUM  MOLLUSCA  251 

After  a  parasitic  life  within  the  tissues  of  the  fish  of  from  three 
to  twelve  weeks  the  young  mussel  is  liberated  and  takes  up  a  free 
existence. 

In  Unio  the  eggs  are  fertilized  during  the  late  spring  and 
summer,  and  the  glochidia  are  discharged  before  the  middle  of 
September.  The  glochidium  of  Unio  is  smajler  than  that  of 
Anodonta  and  is  usually  bookless.  It  does  not  as  a  rule  be- 
come permanently  attached  to  the  fins,  operculum,  or  mouth 
as  in  Anodonta,  but  usually  lodges  on  the  gill  filaments  of  the 
fish. 

One  result  of  the  parasitic  habit  of  larval  mussels  is  the  dis- 
persal of  the  species  through  the  migrations  of  the  fish.  Only 
in  this  way  can  we  account  for  the  rapid  colonization  of  certain 
streams  by  mussels,  since  the  adult  plows  its  way  through  the 
muddy  bottom  very  slowly. 

Economic  Importance.  —  Fresh-water  mussels  are  of  con- 
siderable importance  in  certain  parts  of  this  country,  especially 
in  Iowa  and  Illinois,  because  their  shells  are  used  extensively  in 
the  manufacture  of  pearl  buttons.  Often,  also,  pearls  of  con- 
siderable value  are  found  in  fresh-water  bivalves.  The  de- 
crease in  the  number  of  mussels  in  the  Mississippi  River  and  its 
tributaries  has  led  the  United  States  Bureau  of  Fisheries  to 
investigate  the  possibility  of  artificially  propagating  them  so  as 
to  restock  the  depleted  waters.  It  seems  probable  that  this  can 
be  done  successfully.  Mussels  are  instrumental  in  purifying 
the  water  in  which  they  live  by  using  as  food  the  organic  particles 
contained  in  it. 

2.   Class  I.    Amphineura 

The  Amphineura  are  marine  mollusks  of  wide  distribu- 
tion. Two  rather  distinct  groups  of  animals  belong  to  this 
class. 

Order  i.  Polyplacophora.  — These  are  the  chitons  (Fig.  179, 
A,  B).  They  are  characterized  by  a  broad,  flat  foot  (B,/),  a 
shell  of  eight  transverse  calcareous  pieces  (A),  and  a  row  of  gills 


252 


COLLEGE  ZOOLOGY 


(B,  g)  between  the  mantle  (pa)  and  the  foot  (/).  The  mouth  (m) 
is  at  one  end  and  the  anus  (a)  at  the  other.  Examples:  Ami- 
cula,  Trachydermon,  Chiton. 

The  chitons  are  slow-moving  mollusks  which  live  near  the  sea- 
shore in  shallow  water.     They  are  usually  herbivorous. 

Order  2.  Aplacophora.  —  These  are  worm-like  mollusks 
(Fig.  179,  C)  without  a  shell,  but  with  many  calcified  spicules  over 


Fig.  1 70.  —  Chitones.  A,  upper  surface  of  Onithochiton.  B,  under  sur- 
face of  Lepidopleurus.  a,  anus ;  /,  f oot ;  g,  gills;  w,  .mouth ;  pa,  mantle; 
te,  pallial  tentacles.  C,  ventral  view  of  Paramenia,  h,  mouth;  si,  foot  groove. 
(A  from  Tryon;    B  and  C,  from  Lankester's  Treatise.) 

the  surface.     The  mantle  surrounds  the  entire  body,  and  the  foot 
lies  in  a  groove  {si).     Example:    Chcetoderma. 

The  Aplacophora  live  on  coral  polyps  and  hydroids.  They 
are  most  abundant  at  a  depth  of  about  fifty  fathoms. 


3.   Class  II.    Gastropoda 

The  snails,  slugs,  limpets,  and  other  similar  mollusks  belong- 
ing to  this  class  possess  a  foot,  a  mantle,  and  a  mantle  cavity 
comparable  with  those  of  the  mussel  (Fig.  172,  I-II),  but  they 
differ  considerably  in  the  form  and  structure  of  their  bodies  as 
well  as  in  their  life-histories.  Three  pecuHarities  are  characteris- 
tic of  most  Gastropoda:  (i)  asymmetry,  (2)  a  well-developed 
head,  and  (3)  frequently  a  spirally  coiled  shell  formed  of  one 
piece. 


PHYLUM  MOLLUSCA 


253 


a.     A  Land-snail 


External  Features.  —  The  body  of  a  snail  consists  of  a  head 
(Fig.  180,  A^^.),  neck,  foot  (F),  and  visceral  hump.  The  head  bears 
two  psiiis  oi  tentacles  {Fii.):  (i)  a*  short  anterior  pair  containing 
the  olfactory  nerves,  and  (2)  a  longer  pair  containing  the  eyes. 
The  mouth  (M.)  is  in  front  and  below  the  tentacles,  and  just 
beneath  the  mouth  is  the  opening  of  the  pedal  mucous  gland. 
The  foot  is  broad  and  flat  (F) ;  it  is  a  muscular  organ  of  locomo- 
tion with  a  mucous- 
secreting  integu- 
ment. Both  the 
foot  and  head  may 
be  withdrawn  into 
the  shell. 

The  spiral  shell 
encloses  the  visceral 
hump,  consisting  of 
parts  of  the  diges- 
tive, circulatory, 
respiratory,  excre- 
tory, and  repro- 
ductive systems. 
The  mantle  (Fig.  180,  Mt.)  lines  the  shell,  and  is  thin  except 
where  it  joins  the  foot;  here  it  forms  a  thick  collar  which 
secretes  most  of  the  shell.  An  opening  beneath  this  collar  is 
the  respiratory  aperture  (At)  leading  into  the  mantle  cavity. 
The  anus  (A)  opens  just  back  of  this  aperture.  The  genital 
pore  is  on  the  side  of  the  head. 

Anatomy  and  Physiology.  —  Digestion.  —  The  general  anat- 
omy of  a  snail  is  shown  in  Figure  181.  The  digestive  organs 
include  a  buccal  mass,  oesophagus  (2),  salivary  glands  (j),  crop^ 
stomach  {4),  digestive  glands  (5),  intestine,  rectum  (6),  and  anus  (7). 

The  food  is  chiefly,  if  not  entirely,  vegetation,  such  as  lettuce. 
This  is  scraped  up  by  a  horny  jaw  or  mandible  and  devoured  after 


Fig.  180.  —  Diagram  showing  the  structure  of  a 
snail.  A,  anus;  At,  respiratory  aperture,  the  en- 
trance to  mantle  cavity  indicated  by  arrow;  D.,  in- 
testine; F,  foot;  J^ii.,  tentacles;  Ko.,  head;  M.,  mouth; 
Mh,  mantle  cavity;  Mt.,  mantle;  R.Mt.,  free  edge  of 
mantle;    Sch.,  shell.     (From  Schmeil.) 


254 


COLLEGE  ZOOLOGY 


13  — 


Fig.  1 8 1.  — Diagram  showing  the  anatomy  of  a  snail,  IleUx  pomatia. 
I,  pharynx;  2,  cesophagus;  5,  salivary  glands;  4,  stomach;  5,  liver;  6,  rectum; 
7,  anus;  8,  kidney;  q,  ureter;  10,  opening  of  ureter;  //,  ventricle;  12,  auricle; 
13,  pulmonary  vein;  14,  opening  of  nephridium  into  pericardium;  15,  ovo- 
testis;  16,  common  duct  of  ovotestis;  17,  albumen  gland;.  18,  female  duct; 
ig,  male  duct;  20,  spermatheca;  21,  flagellum;  22,  accessory  glands;  23,  penis; 
24,  dart  sac;  25,  vagina;  26,  eye  tentacle  retracted;  27,  anterior  tentacle 
retracted;  28,  muscle  which  retracts  head,  pharynx,  tentacle,  etc.  (From 
Shipley  and  MacBride,  after  Hatschek  and  Cori.) 


PHYLUM   MOLLUSCA  255 

being  rasped  into  fine  particles  by  a  band  of  teeth  termed  the 
radula  (Fig.  182).  The  radula  and  the  cartilages  and  muscles 
that  move  it  backward  and  forward  constitute  the  buccal  mass. 
The  salivary  glands  (Fig.  181,  j)  which  lie  one  on  either  side  of 
the  crop  pour  their  secretion  by  Aeans  of  the  salivary  ducts  into 
the  buccal  cavity,  where  it  is  mixed  with  the  food. 

The  (Esophagus  (2)  leads  to  the  crop,  and  from  here  the  food 
enters  the  stomach  (4).  The  two  digestive  glands  (5)  occupy  a 
large  part  of  the  visceral 

hump.     They  secrete  a  /^^^^ 

diastatic  ferment  which  J^^^^^ 

converts  starchy  matters  j^P    rr/Hh 

into    glucose,    and    are  >^F^  '"'Q'  viP^ 

comparable  to  the  pan-  ^^^         • 

creas  in  vertebrate  ani-  ^4^^^ 

mals.       This     secretion  v'^^^^TCL 

enters  the  stomach  and  >t<5^^^^  '/JLvMaN 

aids  in  digestion.     Ab-  j^^y  ^^\ 

sorption      takes      place       /^^^ 
chiefly  in  the  intestine,     ^^ 
and  the  faeces  pass  out    ^ff^ 

through   the   anus    (Fig.         ^^^    ,82. -Part    of    the   radula    of    Physa 

180,  A',   Fig.  181,  7).  fontinalis,  with  central  tooth  and  two  marginal 

Circulation    and    ^f^^^^^^^^j^^^^^^  (From  the  Cambridge 

Respiration.  —  The 

blood  of  the  snail  consists  of  a  colorless  plasma  containing 
corpuscles,  and  serves  to  transport  nutriment,  oxygen,  and 
waste  products  from  one  part  of  the  body  to  another.  The 
heart  lies  in  the  pericardial  cavity  (Fig.  181,  14).  The  muscular 
ventricle  (ii)  forces  the  blood  through  the  blood-vessels  by 
rhythmical  pulsations.  One  large  aorta  arises  at  the  apex  of  the 
ventricle;  this  gives  rise  at  once  to  a  posterior  branch,  which 
suppHes  chiefly  the  digestive  gland,  stomach,  and  ovotestis,  and 
an  anterior  branch  which  carries  blood  to  the  head  and  foot. 
The  blood  passes  from  the  arterial  capillaries  into  venous  capiU 


256 


COLLEGE  ZOOLOGY 


laries  and  flows  through  these  into  sinuses.  Veins  lead  from 
these  sinuses  to  the  walls  of  the  mantle  cavity,  where  the  blood, 
after  taking  in  oxygen  and  giving  off  carbon  dioxide,  enters  the 
pulmonary  vein  (Fig.  181,  ij)  and  is  carried  to  the  single 
auricle  {12)  and  finally  into  the  ventricle  (//)  again. 

Excretion. — The  glandular  kidney  (Fig.  181,  8)  lies  near 
the  heart.     Its  duct,  the  ureter  or  renal  duct  (p),  runs  along  beside 

the  rectum  and  opens  {10)  near  the 
anus  (7). 

Nervous  System.  —  Most  of  the 
nervous  tissue  of  the  snail  is  concen- 
trated just  back  of  the  buccal  mass 
and  forms  a  ring  about  the  oesoph- 
agus (Fig.  181,  in  black;  Fig.  183). 
There  are  five  sets  of  gangUa  and 
four  ganglionic  swellings.  The  supra- 
cesophageal  or  cerebral  ganglia  (Fig. 
183,  4)  are  paired  and  lie  above  the 
oesophagus.  Nerves  extend  anteri- 
orly from  them,  ending  in  the  two 
buccal  ganglia  (i),  the  two  eyes,  the 
two  ocular  ganglionic  swellings  (j),  the 
Fig.  183.  — Central  portion   two  olfactory  ganglionic  swelHngs,  and 

of  the  nervous  system  of  Helix    ,,  .^         -k^  hi 

pomatia.  i,  buccal  ganglion;  the  mouth.  Nerves  Called  commis- 
2,  optic  nerve  with  thickened  sures   Connect   the   supra-oesophageal 

root  (5)  arising  from  the  cere-  ,.  .,,      ,,  ,.  ,  .   ,      ,. 

bral  ganglion  (4);  5.  pedai,  ganglia  With  the  ganglia  which  lie 
6,  pleural,  7,  parietal,  8,  vis-  beneath   the   oesophagus.      Here   are 

ceral.  ganglion.     (From  Lang,    -  .  -  ,.      ,    .  , 

after  Bohmig  and  Leuckart.)      ^OMX  pairs  of  ganglia  lying  close  to- 
gether—  the   pedal    (5),  pleural    (<5), 
parietal  (7),  and  visceral  (8).     Nerves  pass  from  them  to  the 
visceral  hump  and  the  basal  parts  of  the  body. 

Sense-organs.  —  Both  the  foot  and  the  tentacles  are  sensitive 
to  contact,  and  are  liberally  supplied  with  nerves.  Each  long 
tentacle  (Fig.  180,  Fii.)  bears  an  eye.  These  eyes  are  probably 
not  organs  of  sight,  but  only  sensitive  to  light  of  certain  intensities. 


PHYLUM   MOLLUSCA  257 

Many  snails  feed  mostly  at  night,  and  their  eyes  may  be  adapted 
to  dim  light. 

Snails  possess  a  sense  of  smell,  since  some  of  them  are  able  to 
locate  food,  which  is  hidden  from  sight,  at  a  distance  of  eighteen 
inches.  We  are  not  certain  where  the  sense  of  smell  is  located, 
but  investigators  are  inclined  to  believe  that  the  small  tentacles 
(Fig.  180)  are  the  olfactory  organs.     A  sense  of  taste  is  doubtful. 

There  are  two  organs  of  equilibrium  (statocysts) ,  one  on  either 
side  of  the  supra-oesophageal  ganglia.  They  are  minute  vesicles 
containing  a  fluid  in  which  are  suspended  small  calcareous  bodies 
(statoliths).  Nerves  connect  them  with  the  supra-cesophageal 
gangHa. 

Locomotion.  —  The  snail  moves  from  place  to  place  with 
a  gliding  motion.  The  slime  gland  which  opens  just  beneath 
the  mouth  deposits  a  film  of  slime,  and  on  this  the  animal  moves 
by  means  of  wave-like  contractions  of  the  longitudinal  muscular 
fibers  of  the  foot.  Snails  have  been  observed  to  travel  two 
inches  per  minute  (Baker). 

Reproduction.  —  Some  gastropods  are  dioecious;  others  are 
monoecious.  Helix  is  hermaphroditic,  but  the  union  of  two 
animals  is  necessary  for  the  fertilization  of  the  eggs,  since  the 
spermatozoa  of  an  individual  do  not  unite  with  the  eggs  of  the 
same  animal.  The  spermatozoa  arise  in  the  ovotestis  (Fig.  181, 
75);  they  pass  through  the  coiled  hermaphroditic  duct  (16)  and 
into  the  sperm  duct;  they  then  enter  the  vas  deferens  (zp)  and  are 
transferred  to  the  vagina  (25)  of  another  animal  by  means  of  a 
cylindrical  penis  (25)  which  is  protruded  from  the  genital  pore. 

The  eggs  also  arise  in  the  ovotestis  and  are  carried  through  the 
hermaphroditic  duct;  they  receive  material  from  the  albumen 
gland  (17)  and  then  pass  into  the  uterine  canal ;  they  move  from 
here  down  the  oviduct  {18)  into  the  vagina  (25),  where  they  are 
fertilized  by  spermatozoa  which  were  transferred  to  the  seminal 
receptacle  {20)  by  another  snail.  In  almost  all  other  land  pul- 
monates  impregnation  is  mutual,  each  animal  acting  during 
copulation  as  both  male  and  female. 


258  COLLEGE  ZOOLOGY 

b.   Gastropoda  in  General 

Classification.  —  There  is  considerable  diversity  among  gas- 
tropods both  in  form  and  structure.  The  chief  characteristics 
used  in  dividing  them  into  groups  are  the  structure  of  the 
nervous  system,  the  method  of  respiration  and  structure  of  the 
respiratory  organs,  and  the  condition  of  the  sexual  organs. 
There  are  two  subclasses,  each  containing  two  orders. 

Subclass  I.  Streptoneura.  —  Dioecious  Gastropoda  with 
visceral  connectives  usually  twisted  into  a  figure  8;  the  heart  is 
usually  posterior  to  the  gills. 

Order  i.  Aspidobranchia.  Streptoneura  with  usually  two 
gills,  two  auricles,  and  two  nephridia.  Examples:  Acmcea 
(limpet),  Haliotis  (ear-shell),  Margarita. 

Order  2.  Pectinibranchia.  Streptoneura  with  one  kidney, 
one  auricle,  and  one  gill.  Examples:  Littorina,  Sycotypus  (Fig. 
186,  A),  Crepidula  (Fig.  186,  B),  Urosalpinx. 

Subclass  II.  Euthyneura.  Monoecious  Gastropoda  with 
visceral  connectives  not  twisted  (Fig.  183) ;  the  gill  when  present 
is  posterior  to  the  heart. 

Order  i.  Opisthobranchia.  Marine  Euthyneura  usually 
with  a  gill  and  mantle.     Examples:   Bulla,  Clione,  Doris. 

Order  2.  Piilmonata.  Land  and  fresh- water  Euthyneura 
which  breathe  air;  gill  ustially  aborted  and  mantle  cavity  con- 
verted into  a  lung.  Examples:  Helix,  Polygyra  (Fig.  185,  C), 
LymncBa  (Fig.  185,  G),  Limax  (Fig.  184),  Physa  (Fig.  185,  D), 
PU/norhis  (Fig.  185,  B). 

/Air-breathing  Gastropods.  —  The  air-breathing  gastropods 
^belong  chiefly  to  the  order  Pulmonata,  and  inhabit  fresh  water 
or  live  on  land.  The  slugs  also  live  on  land,  but  are  without  a 
well-developed  shell.  Limax  maximus  (Fig.  184)  is  a  large  slug. 
It  was  introduced  from  Europe  and  is  now  more  or  less  of  a  pest 
in  greenhouses  because  of  its  fondness  for  green  leaves.  The 
shell  of  Limax  is  a  thin  plate  embedded  in  the  mantle. 

Three  common  fresh-water  snails  with  shells  are  Physa,  Lym- 


PHYLUM   MOLLUSCA 


259 


ncea,  and  Planorbis.  Physa  (Fig.  185,  D)  lives  in  ponds  and 
brooks  and  feeds  on  vegetable  matter.  It  is  a  sinistral  snail, 
since  if  the  shell  is  held 
so  that  the  opening  faces 
the  observer  and  the  spire 
points  upward,  the  aper- 
ture will  be  on  the  left. 
LymncEa  (Fig.  185,  G)  is 
the  common  pond-snail. 
Its  shell  is  coiled  in  an 
opposite  direction  from 
that  of  Physa  and  is 
called  dextral.  Both 
Physa  and  Lymncsa  usu- 
ally come  to  the  surface 
to  breathe.  In  dry  weather  many  snails  have  the  power  of  se- 
creting a  mucous  epiphragm  over  the  mouth  of  the  shell  so  as  to 


Fig.  184.  —  Limax  maximus.  PO,  pul- 
monary orifice.  (From  the  Cambridge 
Natural  History.) 


Fig.  185.  — The  shells  of  certain  Gastropoda.  A,  Helicodiscus  parallelus. 
B,  Planorbis  trivolvis.  C,  Polygyra  albolabris.  D,  Physa  gyrina.  E,  Pleuro- 
cera  elevatum.  F,  Goniobasis  liviscens.  G,  Lymncea  palustris.  (From  various 
authors.) 


26o 


COLLEGE  ZOOLOGY 


Fig.  1 86.  —  Two  marine  Gastropods. 
A,  Sycotypus  caniculatus.  B,  Crepidula. 
(A,  from  Davenport ;    B,  from  Weysse.) 


prevent  the  evaporation  of  moisture  from  their  bodies.     Plan- 
orhis  (Fig.  185,  B)  differs  from  Physa  and  Lymncea  in  having  a 

shell  coiled  in  one  plane 
like  a  watchspring. 

Marine  Gastropods.  — 
The  majority  of  the 
marine  gastropods  have 
shells,  but  many  of  them 
do  not ;  some  of  the 
latter  are  called  nvdi- 
branchs.  LiUorina  lit- 
torea,  the  periwinkle,  is 
a  very  common  shelled 
snail  on  the  North  At- 
lantic sea-shore.  It  was 
introduced  from  Europe, 
where  in  many  localities 
it  is  used  as  an  article  of 
food  by  the  natives.  In  Crepidula  (Fig.  186,  B)  the  spiral  has 
almost  disappeared,  and  the  shell  is  boatlike.  AcmcBa,  the 
limpet,  is  a  sea-snail  modified  so  as  to  cling  closely  to  rocks.  Its 
shell  is  conical.  In  Europe  limpets  are  used  as  food.  Sycotypus 
(Fig.  186,  A)  is  a  very  large  marine  gastro- 
pod that  lives  in  shallow  water  and  feeds 
on  other  moUusks.  Urosalpinx,  the  oyster 
drill,  and  several  other  marine  snails,  make 
a  practice  of  boring  through  the  thick  shells 
of  oysters  and  other  bivalves  with  their 
radulas  and  taking  out  the  soft  body  of 
the  victims  through  the  hole. 

The  term  nudihranch  is  applied  to  certain 
shell-less   marine    gastropods.     The   nudi- 
branchs    resemble    the    terrestrial    slugs ; 
they  do  not  breathe  air,  however,  but  take   3k!"ch!'L«..*  (fZ" 
oxygen  from  the  water  by  means  of  naked   Davenport.) 


PHYLUM   MOLLUSCA 


261 


gills,  or  through  the  mantle.     Eolis  (Fig.  187)  and  Dendronotus 
are  common  genera. 

The  shelled  marine  Gastropoda  usually  breathe  by  means  of 
gills.  In  Sycotypus,  for  example,  there  is  a  trough-like  extension 
of  the  collar,  the  siphon,  which  leads  a  current 
of  water  into  the  mantle  cavity  where  the  gill 
is  situated.  The  direction  of  this  current  of 
water  prevents  contamination  by  the  faeces 
and  excretory  products. 

4.  Class  III.    Scaphopoda 

This  class  contains  only  a  few  aberrant 
marine  moUusks  called  tooth  shells.  The 
mantle  forms  a  tube  around  the  body  and 
secretes  a  crescent- shaped  tubular  calcareous 
shell  larger  at  one  end  than  at  the  other. 
Both  ends  of  the  shell  are  open.  The  foot 
(Fig.  188,/),  which  is  used  for  boring  in  the 
sand,  can  be  protruded  from  the  larger 
anterior  aperture.  The  head  is  rudimentary, 
but  a  radula  is  present.  Eyes  and  a  heart 
are  absent.  The  sexes  are  separate.  Ex- 
ample: Dentalium  (Fig.  188). 


5.   Class  IV.    Pelecypoda 


Fig.  188.  — ASca- 
PHOPOD,  Dentalium. 
a,  anterior  aperture 
of  mantle ;  /,  foot ; 
g,  genital  gland; 
k,  kidney ;  /,  liver. 
(From    the     Cam- 

The  Pelecypoda  or  Lamellibranchiata,  bridge  Natural  His- 
as  they  are  often  called,  are  the  mussels,  outhiers.^ 
clams,  oysters,  and  other  bivalves.  They 
are  simple  in  structure  and  therefore  favorite  moUusks  for  lab- 
oratory dissection  (pp.  243  to  251),  but  are  probably  less  prim- 
itive than  the  Gastropoda.  They  do  not  possess  a  head  or 
radula.  The  mantle  is  bilobed  and  secretes  a  bivalve  shell.  The 
gills  are  usually  lamellate. 

The  Pelecypoda  are  all  aquatic  and  mostly  marine.     They 


262 


COLLEGE  ZOOLOGY 


feed  on  minute  organisms.  Most  of  them  burrow  into  the  sand 
or  mud;  a  few  bore  cavities  for  themselves  in  calcareous  rocks; 
and  still  others  are  sessile,  like  the  oyster.  Some  Pelecypoda 
live  commensally  or  parasitically  on  or  in  the  bodies  of  ascidians, 
sponges,  and  echinoderms. 

Classification.  —  The  Pelecypoda  are  divided  into  four  orders 
according  to  the  structure  of  the  gills. 

Order  i.  Protobranchia  (Fig.  189,  A).  Pelecypoda  with 
plate-like  gill  filaments  (e,  i)  which  are  not  reflected;    mantle 


Fig.  189.  —  Morphology  of  the  gills  of  Pelecypoda,  seen  diagrammatically 
in  section.  A,  Protobranchia.  B,  Filibranchia.  C,  Eulamellibranchia. 
D,  Septibranchia.  e,  e,  external  row  of  filaments;  i,  i,  internal  row  of  fila- 
ments; e',  external  row  or  plate  folded  back;  i',  internal  row  folded  back; 
/,  foot;  m,  mantle;  s,  septum;  v,  visceral  mass.  (From  the  Cambridge  Natural 
History,  after  Lang.) 


cavity  not  divided  into  two  parts.  Examples:  Nucula,  Leda, 
Yoldia. 

Order  2.  Filibranchia  (Fig.  189,  B).  Pelecypoda  with  gill 
filaments  reflected  and  united  by  ciliary  junctions.  Examples: 
Area,  Mytilus,  Modiola,  Pecten. 

Order  3.  Eulamellibranchia  (Fig.  189,  C).  Pelecypoda 
with  gill  filaments  forming  plates  or  lamellae.  Examples:  Ostrea, 
Cyclas,  Unto,  Anodonta,  Mactra,  Venus,  My  a,  Teredo  (Fig.  190), 
Solen. 

Order  4.  Septibranchia  (Fig.  189,  D).  Pelecypoda  with 
gills  transformed  into  a  muscular  septum  {s)  and  not  functioning 
as  respiratory  organs.     Examples:   Silenia,  Cuspidaria. 


PHYLUM   MOLLUSCA 


263 


Economic  Importance.  —  Several  of 
considerable  importance  as  food  for 
man.  The  most  valuable  are  the 
oyster  and  the  long-neck  or  soft-shell 
clam.  Razor-shells,  hen-clams,  n^us- 
sels,  scallops,  and  a  nmnber  of  other 
bivalves  are  also  eaten. 

The  oyster,  Ostrea  virginiana,  in- 
habits the  shallow  water  along  the 
Atlantic  coast  from  Massachusetts  to 
Florida.  It  is  attached  to  rocks  and 
other  objects  by  its  left  valve,  and 
does  not  move  about  in  the  adult 
stage.  The  Chesapeake  Bay  oyster- 
beds  are  large  and  important.  The 
value  of  the  oyster  industry  along 
the  Atlantic  seaboard  is  from  twenty 
to  thirty  million  dollars  annually. 
Oysters  lay  an  enormous  number  of 
eggs.  Professor  Brooks  placed  the 
number  for  a  single  female  in  one 
season  at  nine  million  or  more. 
Those  eggs  which  are  fertilized  and 
not  eaten  by  fishes  and  other  animals 
develop  into  free-swimming  larvae 
.which  soon  become  fixed  to  some 
object  and  grow  into  the  adults. 
The  larvae  are  preyed  upon  by  many 
animals,  especially  crabs  (Chap. XIII). 
Those  that  reach  the  adult  stage 
may  be  attacked  by  starfishes 
(p.  196),  boring  snails  (p.  260), 
sponges  (p.   106),  and  parasites. 

The  value  of  the  pearl-button  in- 
dustry has  already  been  mentioned 


the  Pelecypoda  are  of 


Fig.  190.  —  A  ship  "  worm," 
Teredo  navalis,  in  a  piece  of 
timber.  P,  pallets;  SS,  si- 
phons ;  T,  tube ;  U,  valves 
of  shell.  (From  the  Cam- 
bridge Natural  History,  after 
Mobius.) 


264  COLLEGE  ZOOLOGY 

(p.  251).  Pearl- fishing  should  also  be  noted.  Pearls  are  pro- 
duced by  secretions  of  the  mantle  around  a  foreign  substance, 
such  as  a  grain  of  sand  or  a  parasitic  worm.  The  Pelecypoda 
of  the  Persian  Gulf  yield  the  finest  pearls. 

One  bivalve,  the  shipworm,  Teredo  navalis  (Fig.  190),  is  in- 
jurious to  ships  and  piles.  It  burrows  into  the  wood  with  its 
shell,  sometimes  to  a  depth  of  two  feet. 

6.   Class  V.    Cephalopoda 

The  Cephalopoda  are  the  squids,  octopods,  and  nautili.  They 
are  constructed  on  the  same  fundamental  plan  as  other  moUusks 
(Fig.  172,  III),  but  are  very  different  in  form  and  habits. 

a.  The  Common  Squid  —  Loligo 

Loligo  pealii  (Fig.  191)  is  one  of  the  common  squids  found 
along  the  eastern  coast  of  North  America  from  Maine  to  South 
Carolina.  It  probably  lives  in  deep  water  during  the  winter, 
but  about  May  i  it  enters  shallow  water  in  large  schools  to  lay 
its  eggs.  Squids  are  of  some  economic  importance,  since  they 
are  used  as  food  by  Chinese  and  Italians,  and  as  bait  for  line  and 
trawl  fishing.  They  feed  on  small  fish,  Crustacea,  and  other 
squids,  and  in  turn  furnish  food  for  cod  and  other  large  fish. 

Anatomy  and  Physiology,  —  The  body  of  Loligo  is  spindle- 
shaped.  When  swimming  through  the  water  the  morphological 
ventral  surface  is  usually  anterior  (Fig.  191,  V);  the  dorsal  sur- 
face is  posterior  (D);  the  anterior  surface  is  dorsal  (A);  and 
the  posterior  surface  is  ventral  (P).  The  skin  may  change  color 
rapidly;  sometimes  it  is  bluish  white,  at  others,  mottled  red  or 
brown. 

The  foot  consists  of  ten  lobes  (Fig.  191,  5,  d,  7)  and  a,  funnel  (j). 
Eight  of  the  lobes  are  arms  (5,  7)  and  two  are  long  tentacles  (6). 
The  inner  surfaces  of  both  arms  and  tentacles  are  provided  with 
suckers.  The  arms  are  pressed  together  and  used  for  steering 
when  the  squid  swims,  but  when  capturing  prey  the  tentacles  are 


PHYLUM   MOLLUSCA 


265 


extended,  seize  the  victim  with  their  suckers,  and  draw  it  back 
to  the  arms,  which  hold  it  firmly  to  the  mouth.  The  funnel  (j) 
is  a  muscular  tube  extending  out  be- 
yond the  edge  of  the  mantle  collar  {2,  g) 
beneath  the  head  {4).  Water*  is  ex- 
pelled from  the  d 
mantle  cavity  (Fig. 
192,  If.  C)  through 
it.  The  funnel  is 
the  principal  steer- 
ing organ;  if  it  is 
directed  forward, 
the  jet  of  water 
passed  through  it 
propels  the  animal 
backward ;  if  di- 
rected backward, 
the  animal  is  pro- 
pelled forward. 

A  thick  muscular 
mantle  endosts  the 
visceral  mass  and 
mantle  cavity.  It 
terminates  ven- 
trally  in  a  collar 
(Fig.  191,  2,  9) 
which  articulates 
with  the  visceral 
mass  and  funnel 
by  three  pairs  of 
interlocking  sur- 
faces. Water  is  drawn  into  the  mantle  cavity  at  the  edge  of 
the  collar  by  the  expansion  of  the  mantle  and  forced  out  through 
the  funnel  by  the  contraction  of  the  mantle.  On  each  side  of 
the  animal  is  a  triangular   fin-like  projection  of  the  mantle 


Fig.  191. — The  squid, 
Loligo  pealii,  side  view. 
A,  anterior;  D,  dorsal; 
P,  posterior;  V,  ventral. 
I,  fin;  2,  edge  of  mantle; 
3,  siphon ;  4,  head ; 
5,  arm;  6,  long  arm  with 
suckers;  7,  arm;  8,  eye; 
Q,  edge  of  mantle.  (From 
Williams.) 


Fig.  192.  —  Diagram 
showing  the  structure  of 
the  squid,  Loligo  pealii. 
A^,  arm;  A*,  long  arm 
with  suckers;  An,  anus; 
Ca,  caecum ;  E,  eye ; 
Gi,  gill ;  Go,  gonad ; 
IS,  ink-sac;  LV,  liver; 
M.  C,  mantle  cavity ; 
iVe,  nephridium;  PA,  phar- 
ynx; Pn,  pen;  5«,  siphon; 
St,  stomach;  SiV,  valve 
of  siphon.  (From  Wil- 
liams.) 


266  COLLEGE  ZOOLOGY 

(Fig.  191,  j);  these  fins  may  propel  the  squid  slowly  forward 
or  backward  by  their  undulatory  movements,  or  may  change 
the  direction  of  the  squid's  progress  by  strong  upward  or 
downward  strokes. 

The  shell  or  pen  of  Loligo  (Fig.  192,  Pn)  is  a  feather-shaped 
plate  concealed  beneath  the  skin  of  the  back  (anterior 
surface). 

The  true  head  is  the  short  region  between  the  arms  and  the 
mantle  collar;   it  contains  two  large  eyes  (E). 

The  digestive  system  includes  a  pharynx  or  buccal  mass  (Fig. 
192,  Ph),  oesophagus,  salivary  glands,  stomach  (St),  c cecum  (Ca), 
intestine,  rectum,  inksac  {IS),  liver,  and  pancreas.  There  are  two 
powerful  chitinous  jaws  in  the  pharynx;  they  resemble  a  par- 
rot's beak  inverted,  and  are  moved  by  strong  muscles.  A  rod- 
ula  is  also  present.  Two  salivary  glands  lie  on  the  dorsal  surface 
of  the  pharynx,  and  one  is  embedded  in  the  ventral  end  of  the 
liver;  they  all  pour  their  secretions  into  the  mouth.  The  oesoph- 
agus leads  from  the  pharynx  through  the  liver  and  into  the  stom- 
ach. Closely  connected  with  the  muscular  stomach  is  the  large, 
thin-walled  caecum.  Food  is  probably  partially  digested  in  the 
stomach  by  fluids  brought  in  from  the  pancreas  and  liver;  it 
then  passes  into  the"  caecum,  where  digestion  is  completed  and 
absorption  takes  place.  Bones  and  other  indigestible  material 
are  forced  from  the  stomach  into  the  intestine  and  out  through 
the  anus  {An). 

The  blood  of  the  squid  is  contained  in  a  double,  closed  vascular ' 
system.  Arterial  blood  is  forced  by  a  muscular  systemic  heart 
to  all  parts  of  the  body  by  three  aortoe:  (i)  anterior,  (2)  posterior, 
and  (3)  genital.  It  passes  from  arterial  capillaries  into  venous 
capillaries,  and  thence  into  the  large  veins.  From  these  it  enters 
the  right  and  left  branchial  hearts,  and  is  then  forced  into  the 
gills  through  the  branchial  arteries.  In  the  gills  the  blood  is 
aerated,  and  is  finally  carried  by  the  branchial  veins  back  to  the 
systemic  heart. 

There  are  two  gills  in  the  squid  (Fig.   192,  Gi).     The  water 


PHYLUjM  mollusca 


267 


which  enters  the  mantle  cavity  flows  over  them,  supplying  oxy- 
gen to  the  blood  and  carrying  away  carbon  dioxide. 

The  two  nephridia  or  kidneys  (Fig.  192,  Ne)  are  white  trian- 
gular bodies  extending  forward  from  the  region  of  the  branchial 
hearts  and  opening  on  either  side^of  the  intestine  at  the  ends  of 
small  papillae. 

The  nervous  system  consists  of  a  number  of  ganglia  mostly  in 
the  head.     The  principal  ones  are  the  supra-oesophageal,  in- 
fra-oesophageal,  suprabuccal,  infrabuccal, 
stellate,  and  optic  ganglia. 

The  sensory  organs  are  two  very  highly 
developed  eyes,  two  statocysts,  and  prob- 
ably an  olfactory  organ.  The  statocysts 
are  two  vesicles  lying  side  by  side  in  the 
head ;    each   contains  a  concretion,    the 

statolith,    and   is   probably   an   organ   of  'MmnM      -p*« 

equilibrium.  The  eyes  (Fig.  192,  E; 
Fig.  193)  are  large  and  somewhat  similar 
superficially  to  those  of  vertebrates  (com- 
pare Fig.  193  with  Fig.  351).  Just  behind 
the  eye  is  a  fold  which  projects  back- 
ward under  the  collar,  and  is  probably 
olfactory. 

Squids  are  either  male  or  female.  The 
reproductive  organs  (Fig.  192,  Go)  of  the 
male    are    the    testis,    a    vas   deferens,   a 

spermatophoric  sac,  which  contains  sperms  bound  together  into 
bundles  called  spermatophores,  and  a  copulatory  organ,  the  penis. 
The  female  organs  are  an  ovary,  oviduct,  oviducal  gland,  and 
nidamental  gland. 

h.  Cephalopoda  in  General 

Classification.  —  The  Cephalopoda  may  be  divided  into  two 
orders  according  to  the  number  of  gills,  kidneys,  and  auricles, 
and  the  character  of  the  shell. 


Fig.  193.  —  Diagram  of 
the  eye  of  a  squid,  Loligo, 
a.o.c,  anterior  optic  cham- 
ber; c,  cornea;  ir,  iris; 
/,  lens;  /',  external  portion 
of  lens;  op.g,  optic  gan- 
glion ;  p.o.c,  posterior 
optic  chamber;  r,  retina. 
(From  the  Cambrid^'e 
Natural  History,  after 
Grenacher.) 


268 


COLLEGE  ZOOLOGY 


Order  i.  Tetrabranchia.  Cephalopoda  with  four  gills,  four 
kidneys,  and  four  auricles;  with  a  large,  external  shell;  no 
suckers;  and  very  short  arms.     Example:   Nautilus  (Fig.  194). 

2 


Fig.  194.  —  The  chambered  nautilus,  Nautilus  pompilius.  i,  last  com- 
pleted chamber  of  shell;  2,  hood  part  of  foot;  3,  shell  muscle;  4,  mantle  cut 
away  to  expose,  5,  the  pinhole  eye;  6,  outer  wall  of  shell,  partly  cut  away  to 
show  chambers;  7,  siphon;  8,  lobes  of  foot;  g,  funnel.  (From  Shipley  and 
MacBride,  after  Kerr.) 

Order  2.  Dibranchia.  Cephalopoda  with  two  gills,  two 
kidneys,  and  two  auricles;   with  shell  enveloped  by  the  mantle; 

and  long  arms  provided  with 
suckers. 

Suborder  i.  Decapoda. 
Dibranchia  with  ten  arms 
—  two  long  and  eight  short. 
Examples:  Loligo  (Fig.  191), 
Ommastrephes,  Rossia. 

Suborder  2.  Octopoda. 
Dibranchia  with  eight  arms 
of  equal  length.  Examples: 
Octopus  (Fig.  196),  Alloposus. 

Nautili.  —  There  are  only 
a  few  living  species  belong- 
ing to  the  genus  Nautilus  in 


Fig.  195.  —  The  paper  nautilus,  Argo- 
nauta  argo  (female),  swimmin'g.  (From 
Sedgwick.) 


PHYLUM   MOLLUSCA 


269 


the  order  Tetrabranchia.  The  chambered  or  pearly  nautilus, 
Nautilus  pompilius  (Fig.  194),  lives  on  the  bottom  of  the  sea 
near  certain  islands  of  the  South  Pacific.  The  shell  is  spirally 
coiled  in  one  plane  and  is  composed  of  compartments  (7)  of 
different  sizes,  which  were  occupied  by  the  animal  in  successive 
stages  in  its  growth.  The  compartments  are  filled  with  gas 
and  are  connected 
by  a  calcareous 
tube  in  which  is  a 
cylindrical  growth 
of  the  animal  called 
the  siphunde  (Fig. 
194,  7)'  The  gas 
in  the  compart- 
ments counterbal- 
ances the  weight  of 
the  shell. 

Octopods. — The 
OcTOPODA  differ 
from  the  decapods, 

like    LohgO,  m   the  ^^^    196. —The   octopus,  Octopus  vulgaris.     A,  at 

absence  of  the  two  rest;  B,  in  motion.    /,  funnel;  the  arrow  shows  direc- 

Inntr      tpntanilar  ^^^^    °^    propelling    current    of    water.       (From    the 

luiig       LciiLacuiai  Cambridge  Natural  History,  after  Merculiano.) 

arms  (Fig.  191,  6). 

The  paper  nautilus,  Argonauta  argo  (Fig.  195),  is  an  octopod, 
the  female  of  which  secretes  a  delicate,  slightly  coiled  shell. 
The  octopus  or  devil-fish.  Octopus  vulgaris  (Fig.  196),  lives  in  the 
Mediterranean  Sea  and  West  Indies.  It  may  reach  a  length  of 
over  ten  feet  and  a  weight  of  seventy-five  pounds.  Devil- 
fishes have  been  accused  of  serious  attacks  on  man,  but  are  prob- 
ably not  so  bad  as  generally  supposed. 

7.   MoLLUSCA  IN  General 

Morphology.  —  The     Mollusca    are    unsegmented,    triplo- 
blastic  animals  with  bilateral  symmetry  (except  in  most  of  the 


270  COLLEGE  ZOOLOGY 

Gastropoda  and  certain  Pelecypoda).  There  is  usually  a 
ventral  muscular  foot,  a  mantle  fold,  a  radula,  and  a  ccelom. 
The  shell,  if  present,  is  usually  imivalve,  bivalve,  eight-parted, 
or  pen-shaped. 

The  bodies  of  moUusks  are  soft  (Lat.  mollis  =  soft)  and  gen- 
erally covered  by  a  slimy  integument.  They  are  therefore 
fitted  for  life  in  the  water  or  in  moist  places.  In  most  cases  the 
body  is  supported  and  protected  by  a  shell.  As  shown  in  Figure 
172,  the  foot  is  present  in  all  mollusks,  but  is  variously  modified; 
it  enables  the  mussel  to  plow  its  way  through  the  sand,  the  snail 
to  glide  along,  and  the  squid  to  swim  through  the  water  and  cap- 
ture its  prey.  The  mantle  is  a  fold  of  the  body- wall  which  secretes 
the  shell.  If  there  are  two  lobes,  a  bivalve  shell  is  produced,  as 
in  the  mussel.  If  only  one  lobe  is  present,  a  univalve  shell 
is  formed,  as  in  snails.  The  shape  of  the  animal  does  not 
depend  upon  the  shell  so  much  as  upon  the  mantle  which 
secretes  it. 

The  Mollusc  A  possess  a  distinct  ccelom  which  is  usually 
recognizable  in  the  adult  as  (i)  the  pericardial  cavity,  and  (2)  the 
cavities  of  the  reproductive  organs. 

Metabolism.  —  Mollusks  eat  both  vegetable  and  animal  food. 
Jaws  are  present  in  many  of  them,  especially  the  gastropods  and 
cephalopods.  A  rasping  organ,  the  radula  (Fig.  182),  exists  in 
the  buccal  cavity  of  many  mollusks;  it  consists  of  rows  of  chi- 
tinous  teeth  which  tear  up  the  food  by  being  drawn  across  it.  In 
the  stomach  the  food  is  acted  upon  by  secretions  from  the  liver, 
which  is  physiologically  a  hepato-pancreas,  and  may  also  excrete 
waste  products  into  the  alimentary  canal. 

The  cavities  which  contain  the  blood  represent  the  hcemocoel. 
The  blood  is  forced  through  these  cavities  by  the  muscular  con- 
tractions of  the  heart.  Oxygen,  absorbed  food,  and  excretory  sub- 
stances are  transported  by  it.  Respiration  takes  place  either  in 
the  gills  or  in  the  mantle.  Most  of  the  fresh-water  and  land- 
snails  (pulmonate  gastropods)  take  air  into  the  mantle  cavity, 
which  thus  serves  the  purpose  of  a  lung.    The  Pelecypoda, 


PHYLUM   MOLLUSCA 


271 


Cephalopoda,  and  marine  gastropods  breathe  mainly  by  means 
of  gills. 

Reproduction.  —  No  cases  of  asexual  reproduction  have  been 
reported  in  mollusks.  The  sexes  are  usually  separate,  though 
the  members  of  one  entire  subclass  of  Gastropoda  (Euthy- 
neura)  are  hermaphroditic.  The  number  of  eggs  laid  by  some 
mollusks  is  very  great ;  for  example,  9,000,000  in  the  oyster.  In 
all  such  cases  the  eggs  are  subjected  to  the  dangers  of  the  ocean 


Fig.  197.  —  Stages  in  the  development  of  a  mollusk,  Patella.  A,  trocho- 
phore  stage.  /,  foot;  fl,  fiagellum;  m,  mouth;  pac,  postanal  cilia;  ve,  velum. 
B,  veliger  stage,  130  hours  old.  /,  rudimentary  foot;  op,  operculum;  sh,  shell; 
V,  V,  velum.  (A,  from  Lankester's  Treatise,  after  Patten;  B,  from  the  Cam- 
bridge Natural  History,  after  Patten.) 

waves  and  to  numerous  enemies,  and  also  pass  through  a  meta- 
morphosis after  hatching.  Other  mollusks  lay  very  few  eggs, 
for  example,  Lymncea,  twenty  to  one  hundred  ;  Helix,  forty  to  one 
hundred ;  and  Faltidina,  about  fifteen.  These  are  terrestrial  or 
fresh-water  species  whose  eggs  produce  young  in  the  adult  form, 
or,  as  in  Paludina,  the  eggs  hatch  within  the  body  of  the  parent. 
The  development  of  the  eggs  of  most  mollusks  includes  a  tro- 
chophore  stage  (Fig.  197,  A)  which  becomes  a  veliger  larva  (Fig. 
197,  B),  so  called  because  of  the  presence  of  a  band  of  cilia,  the 
velum  iv) ,  in  front  of  the  mouth.     The  velum  is  an  organ  of  loco- 


272 


COLLEGE   ZOOLOGY 


motion  and  is  largely  responsible  for  the  dispersion  of  the  species, 
since,  with  its  help  the  larvae  may  travel  long  distances.  The 
primary  germ-layers  {ectoderm  and  entoderm)  arise  either  by  the 
invagination  of  a  blastula  (Fig.  198,  B)  or  by  the  growing  over 
of  certain  cells  (epibole,  Fig.  198,  C).  The  mesoderm  originates 
in  two  primitive  mesoderm  cells  derived  from  one  of  the  larger 


-rruL 


Fig.  198.  —  Stages  in  the  development  of  moUusks'  eggs.  A,  cleavage  of 
the  egg  of  Crepidula,  showing  the  origin  of  the  first  mesodermic  cell  (mes). 
ma,  macromeres;  mi,  micromeres.  B,  frontal  section  of  an  embryo  of  Paludina, 
showing  gastrulation  by  the  invagination  of  a  blastula  (embolic),  mes.,  meso- 
derm bands;  ud.,  archenteron;  v.,  velum.  C,  an  embryo  of  Crepidula,  showing 
epibolic  gastrulation.  bl.  blastopore;  ec,  ectoderm;  en,  entoderm.  (A  and 
C,  from  Lankester's  Treatise,  after  Conklin ;  B,  from  Korschelt  and  Haider,  after 
Tonniges.) 


cells  {macromeres)  of  the  cleavage  stage  (Fig.  198,  A,  mes). 
Two  mesoderm  hands  (Fig.  198,  B,  mes)  are  produced  by  the  mul- 
tiplication of  the  primitive  mesoderm  cells. 

The  Position  of  the  Mollusks  in  the  Animal  Kingdom.  —  We 
are  not  at  all  certain  as  to  the  relations  of  the  Phylum  Mollusca 
to  other  phyla.  Some  investigators  have  sought  to  derive  the 
mollusks  from  turbellarian-like  ancestors.  Considerable  im- 
portance is  attached  to  the  presence  of  a  trochophore  in  the  de- 


PHYLUM  MOLLUSCA  273 

velopmental  history  of  certain  mollusks,  and  many  embryolo- 
gists  are  inclined  to  consider  this  stage  an  indication  of  the  ances- 
tral condition.  According  to  this  view,  the  mollusks,  annelids, 
and  other  animals  which  pass  through  a  trochophore  stage  in 
their  ontogeny  were  all  derived  frem  a  similar  ancestral  form. 


CHAPTER    XIII 
PHYLUM    ARTHROPODA 

I.  Introduction 

The  Arthropoda  (Gr.  arthron,  a  joint;  pous,  a  foot)  are  the 
crayfishes,  water- fleas,  barnacles,  centipedes,  millipedes,  scor- 
pions, spiders,  mites,  and  insects.  All  of  these  animals  have  a 
common  plan  of  construction,  as  shown  in  Figure  199.  The  body 
consists  of  a  series  of  segments  some  or  all  of  which  bear  jointed 


OS.         jr    sx 


Fig.  199.  —  Diagrammatic  representation  of  the  structure  of  an  Arthropod. 
^,eye;  Z?,  intestine;  F,  antenna;  G,  jointed  limbs;  //,  heart;  M,  mouth  parts; 
iV,  nervous  system;  S,  gullet;  Sk,  chitinous  exoskeleton;  uS,  oS,  supra-  and 
infra-cBsophageal  ganglia.     (From  Schmeil.) 


appendages  (G).  The  body  is  covered  by  a  chitinous  exoskele- 
ton (sk)  secreted  by  the  cells  just  beneath  it.  Within  the  body 
is  a  central  tube,  the  alimentary  canal  (D),  with  an  anterior 
mouth  opening  (at  M)  and  a  posterior  anal  opening.  Dorsal 
to  the  alimentary  canal  is  a  blood-vessel  called  the  heart  (H), 
and  ventral  to  the  alimentary  canal  is  the  nerve-cord  (N). 
There  is  a  ganglionic  mass,  the  brain  (oS),  dorsally  situated  in 
the  head. 

The  Phylum  Arthropoda  includes  a  greater  number  of  species 
than  all  of  the  other  phyla  of  the  animal  kingdom  combined. 

274 


PHYLUM   ARTHROPOD  A  275 

This  number  is  estimated  at  from  one  million  up,  although  only 
about  four  hundred  thousand  species  have  been  described. 

Economically  certain  members  of  this  phylum  are  of  great  im- 
portance. We  need  only  mention  the  lobster  as  an  article  of 
food,  the  honey-bee  as  a  producer  of  honey  and  beeswax,  the  silk- 
worm as  the  source  of  silk,  the  gypsy-moth  caterpillar  as  a  de- 
stroyer of  trees,  and  the  mosquito  and  housefly  as  carriers  of 
disease  germs. 

The  Arthropoda  may  be  grouped  for  convenience  in  the  fol- 
lowing manner :  — 

Phylum  Arthropoda.  Crayfish,  Crabs,  Centipedes,  In- 
sects, Spiders,  Scorpions,  Ticks.  Triploblastic,  bilaterally 
symmetrical  animals;  anus  present;  ccelom  poorly  developed; 
segmented,  somites  usually  more  or  less  dissimilar;  paired, 
jointed  appendages  present  on  all  or  a  part  of  the  somites; 
chitinous  exoskeleton. 

Section  A.  Branchiata.  Mostly  aquatic  Arthropoda 
usually  breathing  by  means  of  gills. 

Class  I.  Crustacea.  Examples:  crayfish  (Fig.  202),  water- 
fiea  (Fig.  211),  barnacle  (Fig.  214),  sow-bug  (Fig.  220). 

Section  B.  Tracheata.  Air-breathing  Arthropoda  with 
tracheae  (Fig.  243). 

Division  i.  Protracheata.  Primitive  trachea tes  which  pos- 
sess nephridia  and  other  annelid  characteristics,  and  tracheae  and 
other  insect  characteristics. 

Class  II.     Onychophora.     Example:    Peripatus  (Fig.  228). 

Division  2.  Antennata.  Tracheates  with  one  pair  of  an- 
tennae (Fig.  250). 

Class  III.  Myriapoda.  Antennata  with  many  similar  legs. 
Examples:   centipedes  (Fig.  233),  millipedes  (Fig.  232). 

Class  IV.  Insecta.  Antennata  with  three  pairs  of  legs,  and 
usually  wings.  Examples:  grasshopper  (Fig.  249),  honey-bee 
(Fig.  236). 

Division  j.  Arachnida.  Tracheates  without  antennae,  and 
with  tracheae,  book  lungs,  or  book  gills. 


276 


COLLEGE  ZOOLOGY 


Class  V.     Arachnida.     Examples:   scorpion  (Fig.  318),  spider 
(Fig.  313),  mite  (Fig.  322),  king-crab  (Fig.  327). 

2.   Class  I.    Crustacea 


a.  The  Crayfish  —  Cambarus 

The  crayfish  is  abundant  both  in  this  country  and  in  Europe. 
In  the  eastern  United  States  Cambarus  affinis  is  common. 
Cambarus  virilis  is  plentiful  in  the  Middle  states.  The  European 
crayfish  is  Astacus  (Potomobius)  fluviatilis.  The  anatomy  and 
physiology  of  these  three  species  as  well  as  of  the  lobster  agree 

except  in  minor  de- 
tails, and  the  fol- 
lowing account  may 
be  used  as  a  de- 
scription of  any  of 
them. 

Crayfishes  usu- 
ally hide  by  day  un- 
der rocks  or  logs  at 
the  bottom  of  ponds 
and  streams.  They 
may  be  captured  by 
hand,  with  a  net,  or 
with  a  string  baited 

Fig.   200. — Transverse   section   through   the    ab-        .  , •^^^^(^^r.4- 

domen    of    the    crayfish.       DA,    dorsal    abdominal  With  a piCCe  of  meat, 

artery;     EM,  extensor    muscles    of    the    abdomen;  They   thrive    in    an 

EP,  epimeron;    FM,  flexor    muscles    of    abdomen;  __.„   -..^   and  their 

M,  muscles  of  appendage;  N,  endopodite;  NG,  nerve  aquarmm,  anameir 

ganglion;   P,  protopodite;   PL,  pleuron,  PR,  intes-  entire       lifc-history 

tine;   S,  sternum;    T,  tergum;    V,  ventral  abdominal  ,           Kcor^rorl 

artery;   X,  exopodite.     (From  Marshall  and  Hurst.)  ^^Y     ^^     ODServea 

in  the  laboratory. 
The  yearly  decrease  in  the  number  of  lobsters  available  for 
food,  and  the  steadily  increasing  demand  for  crayfishes,  will 
undoubtedly  soon  make  it  worth  while  to  raise  the  latter  for 
market. 


PHYLUM   ARTHROPODA 


277 


Anatomy  and  Physiology.  —  External  Features.  — The  cray- 
fish is  a  segmented  animal,  but  the  joints  have  been  obUterated 
on  the  dorsal  surface  of  the  ante- 
rior end.  The  body  shows  two 
distinct  regions,  an  anterior  rigid 
portion,  the  cephalothorax.  and  a 
posterior  flexible  qbdQmen.  A 
chitinoiis  exoskcleton,  impregnated 
with  lime  salts,  supports  and  pro- 
tects the  soft  parts  of  the  body. 

A  typical  segment  (Fig.  200) 
consists  of  a  tergum  {T),'2i  sternum 
(5),  two  pleura  (PL),  and  two 
epimera  (EF).  The  cephalo- 
thorax includes  segments  I-XIII; 
a  cervical  groove  separates  the 
cephalic  or  head  region  from  the 
thoracic  region.  The  dorsal 
shield  of  the  cephalothorax  is 
called  the  carapace:  its  anterior 
pointed  extension  is  known  as 
the  rostrum,  and  the  heavy  flap 
on  either  side  protecting  the  gills, 


as    a    branchioste^ite.     There  are    appendages 


-Types    of    crayfish 
A,    foliaceous    type, 
six  segments  and  a  terminal  exten-    second  maxilla.    1-4,  basopodite  ; 

,1,7  '^111  5,    endopodite;     6,    scaphognathite: 

sion,  th^  telsqn,^  m  the  abdomen.      e/>.,  epipodite.    B,  biramous  type, 
Appendages.  —  Each  segment   swimmeret.    ex,  bs.,  protopodite ; 

1  •       f  •    •    ^     1  1  ^^M     exopodite;     en.,     endopodite. 

bears  a  pair  of  jomted  appendages    c-THiir^mous  type,  second  walk- 
which  in  most  cases  differ  from    ^"s    ^^g.     cxp,   bp,    protopodite; 

,  ,  .        .  J     ip,  mp,  cp,  pp,   dp,    segments     of 

the  Other  pairs  in  structure  and    endopodite;  ep.,  epipodite.    (A  and 

function,     but     all     are     probably     C,    from    the    Cambridge    Natural 
.     .  .  ,.  History;       B,     from     Lankester's 

variations    01    a    biramous    type    Treatise.) 

(Fig.   200)   consisting  of  a  basal 

protopodite  (P),  an  inner'  branch,  the  endopodite  (N),  and  an 

outer  branch,  the  exopodite  (X).     Three  types  of  appendages  can 


278 


COLLEGE   ZOOLOGY 


be  distinguished  in  an  adult  crayfish  :    (i)  foliaceous  (second 
maxilla,  Fig.  201,  A),  (2)  biramous  (swimmerets,  Fig.  201,  B), 


and  (3)   uniramous  (walking  legs,  Fig.   201,  C).      Figure   202 
shows  the  position  and  shape  of  most  of  the  appendages,,  and 


PHYLUM  ARTHROPODA 


279 


1 

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ll 
1-^ 

"13 

1 

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ll 

y 

m 

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1 

Q 

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ll 

C/3 

j2 

§ 
i 

fi 

"a 

M 

i2 
g 

1 

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jo 

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Mo 

1 

< 

1 

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u 
__   en 

1^ 

rl 

i 

1^ 

Si 

•  ^  en 

S.S 

Pip 

llj 

*'    TO    ?!^    ♦J 

1 

! 

< 

j 

1—3 
1— 1 

i 

> 

1— 1 

1 

> 

1 
1 

tn 

M 
> 

28o 


COLLEGE  ZOOLOGY 


rj 

o 

'tf.    tn 

-^1 

si 

c 

.^s 

bc"^ 

■.?5  1^ 

,^  ^ 

d  a 

^ 

•5   C   t2 


i2  c  <" 


the  termi- 
forming    a 
pincher 

0 

d 

X5 

M    . 

segme 
nal   t 
power 

10 

< 

bc 
5    be 

C 


(U 


3 


13  =^^  6  a; 

rt    4)    (fl  O 

be  X  -T  «3  ii 


6  « 

P  a 


bJD  « 
en  ^ 


X! 


^   <u  O 

m|3 


O      >H 

a,  1^ 
o  « 

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bC 

C^-. 

15 -^ 

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X 


PHYLUM   ARTHROPODA 


281 


Reduced   in    female;     in 
male,  protopodite   and 
endopodite    fused    to- 
gether, forming  an  or- 
gan    for     transferring 
sperm. 

In    female    as    in    XVI ; 
in   male   modified    for 
transferring    sperm   to 
female 

Creates  current  of  water ; 
in    female     used     for 
attachment  of  eggs  and 
young   ^ 

> 

X 

■g 
B 

In  female  like  exopo- 
dite,  but  longer 

I 

< 

(U 

> 
0 

1 

1 
1 

^  a 

6  1 

<y  ^ 

C 
1— 1 

2 

c 

•2. 

k 
1 

5 

_g 

en 

Flat  oval  plate  divided 
by  transverse  groove 
into  two  parts 

' 

1 

i2 

(N 

l-H 
> 

i 

1 

M 

XIV.  ist  Abdominal 
(ist     Pleopod    or 
Swimmeret) 

XV.  2d    Abdominal 
(2d     Pleopod     or 
Swimmeret) 

XVI.  3d  Abdominal 
(3d     Pleopod    or 
Swimmeret) 

XVII.  4th    Abdom- 
inal (4th  Pleopod 
or  Swimmeret) 

XVIII.  5th  Abdom- 
inal (5  th  Pleopod 
or  Swimmeret) 

1 
g 

•5a 

xB 
>< 

282  COLLEGE  ZOOLOGY 

Table  IX  gives  a  brief  description  of  each  and  the  modifications 
due  to  differences  in  function. 

Internal  Organs.  —  Definite  systems  of  organs  are  present 
in  the  crayfish  for  the  performance  of  the  various  functions. 
The  codom  is  small,  and  is  restricted  to  the  cavities  of  the  repro- 
ductive organs  and  green  glands.  The  cavities  around  the 
alimentary  canal  are  blood  spaces,  and  therefore  represent  a 
hcemocoel.  Some  of  the  organs,  like  the  muscles  and  nervous 
ganglia,  are  seQmentallv  arranged:  others  like  the  excretory 
organs  are  concentrated  in  a  small  space. 

Digestion.  —  Crayfishes  live  chiefly  on  living  snails,  tadpoles, 
young  insects,  and  the  like,  but  sometimes  eat  one  another, 
and  may  also  devour  decaying  organic  matter.  They  feed  at 
night,  being  most  active  at  dusk  and  daybreak.  The  maxilli- 
pedes  and  maxillae  hold  the  food  while  it  is  being  crushed  into 
small  pieces  by  the  mandibles.  The  food  particles  pass -down 
the  ossophams  (Fig.  202,  20)  into  the  anterior,  cardiac  chamber 
of  the  stomach  (21),  where  they  are  ground  up  by  a  number  of 
chitinous  ossicles,  called  the  gastric  mill.  When  fine  enough,  the 
food  passes  through  a  sieve-like  strainer  of  hair-like  setae  into  the 
pyloric  chamber  of  the  stomach  (22);  here  it  is  mixed  with  a 
secretion  from  the  digestive  glands  brought  in  by  the  hepatic 
ducts.  The  dissolved  food  is  absorbed  by  the  walls  of  the  in- 
testine (24).  Undigested  particles  pass  on  into  the  posterior  end 
of  the  intestine,  where  they  are  gathered  together  into  faeces, 
and  egested  through  the  anus  (6). 

Circulation.  —  The  Blood.  —  The  blood  into  which  the 
absorbed  food  passes  is  an  almost  colorless  liquid  in  which  are 
suspended  a  number  of  ameboid  cells,  the  blood  corpuscles  or 
amebocytes.  The  principal  functions  of  the  blood  are  the  trans- 
portation of  food  materials  from  one  part  of  the  body  to  another, 
of  oxygen  from  the  gills  to  the  various  tissues,  of  carbon  dioxide 
to  the  gills,  and  of  urea  to  the  excretory  organs. 

Blood-vessels.  —  The  principal  blood-vessels  are  a  heart, 
seven  arteries,  and  a  number  of  spaces  called  sinuses.     Blood 


PHYLUM   ARTHROPODA  283 

enters  the  heart  from  the  surrounding  sinus  through  three  pairs 
of  valvular  ostia.  Rhythmical  contractions  then  force  it  for- 
ward, backward,  and  downward. 

(i)  The  ophthalmic  artery  (Fig.  202,  54)  supplies  part  of  the 
stomach,  the  oesophagus,  and  head> 

(2,  3)  The  two  antennary  arteries  (jj)  carry  blood  to  the 
stomach,  antennae,  excretory  organs,  and  other  cephalic  tissues. 

(4,  5)  The  two  hepatic  arteries  {j6)  lead  to  the  digestive 
glands. 

(6)  The  dorsal  abdominal  artery  (ji)  supplies  the  intestine  and 
surrounding  tissues. 

(7)  The  sternal  artery  (jo)  divides  into  a  ventral  thoracic  and  a 
ventral  abdominal  artery  which  carry  blood  to  the  appendages 
and  other  ventral  organs. 

Sinuses.  —  The  blood  passes  from  the  arteries  into  spaces 
lying  in  the  midst  of  the  tissues,  called  sinuses.  The  heart  lies 
in  the  pericardial  sinus.  The  thorax  contains  a  large  ventral 
blood  space,  the  sternal  sinus j  and  a  number  of  branchio-cardiac 
canals  extending  from  the  bases  of  the  gills  to  the  pericardial 
sinus.  A  perivisceral  sinus  surrounds  the  alimentary  canal  in  the 
cephalothorax. 

The  Blood  Flow.  —  The  heart,  by  means  of  the  rhythmical 
contractions,  forces  the  blood  through  the  arteries  to  all  parts 
of  the  body.  Valves  are  present  in  every  artery  where  it  leaves 
the  heart;  they  prevent  the  blood  from  flowing  back.  The 
finest  branches  of  these  arteries,  the  capillaries,  open  into  spaces 
between  the  tissues,  and  the  blood  eventually  reaches  the  sternal 
sinus.  From  here  it  passes  into  the  efferent  channels  of  the  gills 
and  into  the  gill  filaments,  where  the  carbonic  acid  in  solution  is 
exchanged  for  oxygen  from  the  water  in  the  branchial  chambers. 
It  then  returns  by  way  of  the  afferent  gill  channels,  passes  into 
the  branchio-cardiac  sinuses,  thence  to  the  pericardial  sinus,  and 
finally  through  the  ostia  into  the  heart.  The  valves  of  the  ostia 
allow  the  blood  to  enter  the  heart,  but  prevent  it  from  flowing 
back  into  the  pericardial  sinus. 


284 


COLLEGE  ZOOLOGY 


Respiration.  —  Between  the  branchiostegites  and  the  body- 
wall  are  the  branchial  chambers  containing  the  resi^jj^tory  organs, 
the  ^ills.  At  the  anterior  end  of  the  branchial  chamber  is  a 
channel  in  which  the  scaphognathite  of  the  second  maxilla  (Fig. 
201,  A  J  6)  moves  back  and  forth,  forcing  the  water  out  through 
the  .anterior  opening.  Fresh  water  flows  in  through  the  poste- 
rior opening  of  the  branchial  chamber. 

Gills.  —  There  are  two  rows  of  gills;  the  outer,  podobranchice^ 
are  fastened  to  the  coxopodites  of  certain  appendages  (see  Table 
X)  and  the  inner  double  row,  the  arthrobranchicB,  arise  from  the 
membranes  at  the  bases  of  these  appendages.  In  Astacus  there 
is  a  third  row,  the  pleurobranchice,  attached  to  the  walls  of  the 
thorax.  The  number  and  arrangement  of  these  gills  are  shown 
in  Table  X.     Each  gill  possesses  a  number  of  gill  filaments. 

TABLE  X 

THE   NUMBER   AND   POSITION   OF   THE    GILLS    OF   THE   CRAYFISH 

(Cambarus) 


Segment 

PODO- 
BRANCHI^ 

Arthrobranchi^ 

Total 

Anterior 

Posterior 

Numbers 

VI 

0  (ep.) 

0 

0 

0  (ep.) 

VII 

0 

2 

VIII 

3 

DC 

3 

X 

3 

XI 

3 

XII 

3 

6  (ep.) 

6 

5 

17  (ep.) 

Excretion.  —  The  waste  products  of  metabolism  are  taken 
from  the  blood  by  a  pair  of  rather  large  bodies,  the  "  pireen 
glands  "  (Fig.  202,  40)  situated  in  the  ventral  part  of  the  head 


PHYLUM   ARTHROPODA 


285 


anterior  to  the  oesophagus.  Each  green 
gland  consists  of  a  glandular  portion, 
green  in  color  (40),  a  thin- walled  dilata- 
tion, the  bladder  {41),  and  a  duct  open- 
ing to  the  exterior  through  a  pore^-at  the 
top  of  the  papilla  on  the  basal  segment 
of  the  antenna  {42). 

Nervous  System.  —  The  morphology 
of  the  nervous  system  of  the  crayfish  is 
in  many  respects  similar  to  that  of  the 
earthworm.  The  central  nervous  system 
includes  a  dorsal  ganglionic  mass,  the 
brain  (Fig.  202,  25),  in  the  head,  and 
two  circumoeso pha  ^eal  connectives  {2:6) 
passing  to  the  yentral  nerve-cord  (27), 
which  lies  near  the  median  ventral  sur- 
face of  the  body.  The  brain  sends 
nerves  to  the  eyes,  antennules,  and  an- 
tennae. Each  segment  posterior  to  VII 
possesses  a  ganglionic  mass,  which  sends 
nerves  to  the  surrounding  tissues.  The 
large  suboesophageal  ganglion  in  segment 
VII  consists  of  the  ganglia  of  segments 
III- VII  fused  together.  It  sends  nerves 
to  the  mandibles,  maxillae,  and  first  and 
second  maxillipeds.  Visceral  nerves  arise 
from  the  brain  and  extend  posteriorly  to 
the  viscera. 

Sense-organs.  —  Eyes.  —  The  eyes  of 
the  crayfish  (Fig.  202,  28)  are  situated  at 
the  end  of  movable  stalks,  one  on  either 
side  of  the  head.  Each  eye  is  covered 
by  a  modified  portion  of  the  chitinous 
cuticle  called  the  cornea.  The  cornea  is 
divided  into  hexagonal  areas  known  as 


Fig.  203. — Longitudinal 
sections  of  two  ommatidia 
of  the  crayfish.  A,  pigment 
arranged  as  influenced  by 
light.  B,  pigment  arranged 
as  influenced  by  darkness. 
I,  cornea ;  2,  nucleus  of 
corneagen  cells;  j,  nucleus 
of  vitrella ;  4,  nucleus  of 
pigment  cell;  5,  crystalline 
cone ;  6,  tapetum  cell ; 
7,  rhabdom;  8,  retinal  cell; 
Q,  basement  membrane ; 
70,  retinal  nerve  fiber. 
(From  Sedgwick's  Zoology, 
after  Parker.) 


286 


COLLEGE  ZOOLOGY 


facets,  which  are  the  ends  of  long  visual  rods,  the  ommatidia. 
The  average  number  of  ommatidia  in  a  single  eye  is  2500. 
The  parts  of  an  ommatidium  are  shown  in  Figure  203. 

Vision.  — The  eyes  of  the  crayfish  are  supposed  to  produce 
an  erect  mosaic  or  "  apposition  image  ";  this  is  illustrated  in 
Figure  204,  where  the  ommatidia  are  represented  by  a~e,  and  the 
fibers  from  the  optic  nerve  by  a'-e\  The  rays  of  light  from  any 
point  a,  b,  or  c  will  all  encounter  the  dark  pigment  cells  surround- 
ing the  ommatidia  and  be  absorbed,  except  the  ray  which  passes 

directly  through  the  center  of 
the  cornea,  as  d  or  e ;  this 
ray  will  penetrate  to  the 
fibers  from  the  optic  nerve. 
One  ommatidium  thus  re- 
ceives a  single  impression, 
and  since  the  ommatidia  are 
directed  to  different,  though 
adjoining,  regions,  the  sum 
Fig  204. -Diagram  to  explain  mosaic  ^£  ^^le  resulting  images  may 

vision  (see  text).     (From  Packard,  after  ^  ^  _ -^ 

Lubbock.)  be   compared    to    a   mosaic. 

This  method  of  image  forma- 
tion is  especially  well  adapted  for  recording  motion,  since  any 
change  in  the  position  of  a  large  object  affects  the  entire  2500 
ommatidia. 

When  the  pigment  surrounds  the  ommatidia  (Fig.  203,  A), 
vision  is  as  described  above;  but  it  has  been  found  that  in  dim 
light  the  pigment  migrates  partly  toward  the  outer  and  partly 
toward  the  basal  end  of  the  ommatidia  (Fig.  203,  B).  When 
this  occurs,  the  ommatidia  no  longer  act  separately,  but  a  com- 
bined image  is  thrown  on  the  retinular  layer. 

Statocysts.  —  The  statocysts  of  Cambarus  are  chitinous- 
lined  sacs  situated  one  in  the  basal  segment  of  each  antennule. 
In  the  statocyst  are  sl  number  of  sensory  hairs,  among  which  are 
a  few  grains  of  sand,  called  statoliths,  placed  there  by  the  cray- 
fish.    The  contact  of  the  statoliths  with  the  hairs  determines 


PHYLUM  ARTHROPODA 


287 


the  orientation  of  the  body  while  swimming.  Statocysts  are, 
therefore,  organs  of  equilibration.  When  the  crayfish  changes 
its  exoskeleton  in  the  process  of  molting,  the  statocyst  is  also 
shed.  Individuals  that  have  just  molted,  or  have  had  their  stato- 
cysts removed,  lose  much  of  theif  powers  of  orientation.  Per- 
haps the  most  convincing  proof  of  the  function  of  equilibration 
is  that  furnished  by  the  experiments  of  Kreidl.  This  investi- 
gator placed  shrimps,  which  had  just  molted  and  were  therefore 
without  statoliths,  in  filtered  water. 
When  supplied  with  iron  filings, 
the  animals  filled  their  statocysts 
with  them.  A  strong  electromag- 
net was  then  held  near  the  stato- 
cyst, and  the  shrimp  took  up  a 
position  corresponding  to  the  re- 
sultant of  the  two  pulls,  that  of 
gravity  and  of  the  magnet. 

Muscular  System.  —  The  prin- 
cipal muscles  in  the  body  of  the 
crayfish  are  situated  in  the  ab- 
domen, and  are  used  to  bend  that 
part  of  the  animal  forward  upon 
the  ventral  surface  of  the  thorax, 
thus  producing  backward  locomo- 
tion in  swimming.      Other  muscles    oviduct;  5,  base  of  third  walking 

extend  the  abdomen  in  the  prepara-  g^-^g  j^^'^''"'  ^^'^^^^  ^""^  ^^"^ 
tion  for  another  stroke.  The  ap- 
pendages are  all  suppUed  wdth  muscles  which  give  them  the 
power  of  motion.  It  is  of  interest  to  note  that  the  muscles 
are  internal,  and  attached  to  the  inner  surface  of  the  skeleton. 
In  man,  on  the  contrary,  the  skeleton  is  internal  and  the  muscles. 
external. 

Reproduction.  —  The  sexes  of  crayfishes  are  normally  sep- 
arate (dioecious).  In  the  male  the  spermatozoa  arise  in  the 
bilobed  testis  (Fig.  202,  jy),  pass  through  the  paired  vasa  defer- 


FiG.  205.  —  Female  reproductive 
organs  of  the  crayfish,  i,  right 
oviduct;  2,  right  lobe  of  ovary; 
3,  left  lobe  opened  to  show  central 
cavity ;     4,    external    opening    of 


288  COLLEGE  ZOOLOGY 

entia  {j8)  and  out  of  the  genital  apertures  (8),  one  in  the  base  of 
each  fifth  walking  leg.  In  the  female  the  eggs  arise  in  the  bilobed 
ovary  (Fig.  205,  2,  j),  pass  through  the  paired  oviducts  (i),  and 
out  of  the  genital  apertures  {4),  one  in  the  base  of  each  third 
walking  leg. 

The  spermatozoa  are  transferred  from  the  male  to  the  seminal 
receptacle  of  the  female  during  copulation,  which  usually  takes 
place  in  the  autumn.  The  seminal  receptacle  is  a  cavity  in  a 
fold  of  cuticle  between  the  fourth  and  fifth  pairs  of  walking  legs. 
The  eggs  are  laid  in  April  and  are  probably  fertilized  by  the 
spermatozoa  at  this  time.     They  are  fastened  with  a  sort  of  glue 


Fig.  206.  —  Female  crayfish  aerating  eggs  by  raising  and  straightening 
abdomen  and  waving  swimmerets  back  and  forth.  (From  Andrews  in  Am. 
Nat.) 


to  the  swimmerets,  and  are  aerated  by  being  moved  back  and 
forth  through  the  water  (Fig.  206). 

The  cleavage  of  the  egg  is  superficial  (Fig.  207,  A),  and  the  em- 
bryo appears  first  as  a  thickening  on  one  side  (Fig.  207,  B). 
The  eggs  hatch  in  from  five  to  eight  weeks,  and  the  larvae  cling 
to  the  egg-shell.  In  about  two  days  they  shed  their  cuticular 
covering,  a  process  known  as  molting  or  ecdysis.  This  casting 
off  of  the  covering  of  the  body  is  not  peculiar  to  the  young,  but 
occurs  in  adult  crayfishes  as  well  as  in  young,  and  adults  of  many 
other  animals.  In  the  larval  crayfish  the  cuticle  of  the  first  stage 
becomes  loosened  and  drops  off.  In  the  meantime,  the  hypo- 
dermal  cells  have  secreted  a  new  covering.  Ecdysis  is  necessary 
before  growth  can  proceed,  since  the  chitin  of  which  the  exo- 
skeleton  is  composed  does  not  allow  expansion.     In  adults  it  is 


PHYLUM   ARTHROPODA 


289 


also  a  means  of  getting  rid  of  an  old  worn-out  coat  and  acquiring 
a  new  one.     The  young  stay  with  the  mother  for  about  one  month, 


v. 


^ 


Fig.  207.  —  Stages  in  the  development  of  the  egg  of  the  crayfish.  A,  super- 
ficial cleavage  of  the  egg.  B,  embryo  in  the  Nauplius  stage.  A,  anus; 
a>,  antennule;  a^,  antenna;  e,  rudiment  of  eye;  /,  upper  lip;  m,  mandible; 
ta,  thoraco-abdominal  plate.     (From  Korschelt  and  Heider,  after  Reichenbach.) 

and  then  shift  for  themselves.  They  molt  at  least  seven  times 
during  the  first  summer.  The  life  of  a  crayfish  usually  extends 
over  a  period  of  three 
or  four  years. 

Regeneration.  —  The 
crayfish  and  many 
other  crustaceans  have 
the  power  of  regenerat- 
ing lost  parts,  but  to  a 
mnr.h  more  limited~ex- 
tent  than  such  animals 


^^ 


N 


-i 


as  Hydra  and  the  earth- 
worm. Experiments 
have  been  performed 
upon  almost  every  one 
of  the  appendages  as 
well  as  the  eye.  The 
growth  of  regenerated  tissue  is  more  frequent  and  rapid  in 
voung  specimens  than  in  adults.  The  new  structure  is  not 
u 


Fig.  208.  —  Diagram  showing  antenna-like 
organ  regenerated  in  place  of  an  eye  of  Palaemon. 
(From  Morgan,  after  Herbst.) 


290  COLLEGE   ZOOLOGY 

always  like  that  of  the  one  removed.  For  example,  Figure  208 
shows  an  antenna  which  regenerated  in  place  of  an  eye  in  a 
marine  crustacean,  Palcsmon. 

Autotomy.  —  Perhaps  the  most  interesting  morphological 
structure  connected  with  the  regenerative  process  in  Camharus 
is  the  definite  breaking  point  near  the  bases  of  the  walking  legs. 
If  the  chelae  are  injured,  they  are  broken  off  by  the  crayfish  at 
the  breaking  point.  The  other  walking  legs,  if  injured,  may  be 
thrown  off  at  the  free  joint  between  the  second  and  third  segments. 
A  new  leg,  as  large  as  the  one  lost,  develops  from  the  end  of  the 
stump  remaining.  This  breaking  off  of  the  legs  at  a  definite, 
point  is  known  as  autotomy.  a  phenomenon  that  also  occurs  in 
a  number  of  other  animals.  The  leg  is  separated  along  the  break- 
ing point  by  several  successive  muscular  contractions.  It  has 
been  shown  "  that  autotomy  is  not  due  to  a  weakness  at  the 
breaking  point,  but  to  a  reflex  action,  and  that  it  may  be  brought 
about  by  a  stimulation  of  the  thoracic  ganglion  as  well  as  by  a 
stimulation  of  the  nerve  of  the  leg  itself."     (Reed.) 

The  power  of  autotomy  is  of  advantage  to  the  crayfish,  since 
the  wound  closes  more  quickly  if  the  leg  is  lost  at  the  breaking 
point.  No  one  has  yet  offered  an  adequate  theory  to  account 
for  autotomy.  It  is  probably  "  a  process  that  the  animal  has 
acquired  in  connection  with  the  condition  under  which  it  lives, 
or,  in  other  words,  an  adaptive  response  of  the  organism  to  its 
condition  of  life."     (Morgan.) 

Behavior.  —  When  at  rest,  the  crayfish  usually  faces  the  en- 
trance to  its  place  of  concealment,  and  extends  its  antennae.  It 
is  thus  in  a  position  to  learn  the  nature  of  an  approaching  object 
without  being  detected.  Activity  at  this  time  is  reduced  to 
the  movements  of  a  few  of  the  appendages  and  the  gills;  the 
scaphognathites  of  the  second  maxillae  move  back  and  forth, 
baling  water  out  of  the  forward  end  of  the  gill  chambers;  the 
swimmerets  are  in  constant  motion  creating  a  current  of  water; 
the  maxillipeds  are  likewise  kept  moving;  and  the  antennae  and 
eye-stalks  bend  from  place  to  place. 


PHYLUM   ARTHROPODA 


291 


Locomotion.  —  Locomotion  is  effected  in  two  ways,  walking 
and  swimming.  Crayfishes  are  able  to  walk  in  any  direction, 
forward  usually,  but  also  sidewise,  obliquely,  or  backward. 
Swimmins.  is  not  resorted  to  under  ordinary  conditions,  but  only 
when  the  animal  is  frightened  or  shocked.  In  such  a  case  the 
crayfish  extends  the  abdomen,  spreads  out  the  uropod  and  tel- 
son,  and,  by  sudden  contractions  of  the  bundles  of  flexor  abdom- 
inal muscles,  bends  the  abdomen  and  darts  backward.  The 
.swimming  reaction  apparently  is  not  voluntary,  but  is  almost 
entirely  reflex.  If  turned  over  on  its  back,  the  crayfish  either 
raises  itself  on  one  side  and  topples  over,  or  else  gives  a  quick 
backward  flop. 

Reactions  to  Stimuli.  —  Thigmotropism.  —  The  crayfish 
^^is  sensitive  to  touch  over  the  whole  surf  ace  of  the  body,  but  es- 
pecially on  the  chelae  and  chelipedes,  the  mouth  parts,  the  ven- 
tral surface  of  the  abdomen,  and  the  edge  of  the  telson."     (Bell.) 

Positive  thigmotropism  is  exhibited  by  crayfishes  to  a  marked 
degree,  the  animals  seeking  to  place  their  bodies  in  contact  with 
a  solid  object,  if  possible.  The  normal  position  of  the  crayfish 
when  at  rest  under  a  stone  is  such  as  to  bring  its  sides  or  dorsal 
surface  in  contact  with  the  walls  of  its  hiding  place.  Thigmot- 
ropism, no  doubt,  is  of  distinct  advantage,  since  it  forces  the 
animal  into  a  place  of  safety. 

Chemotropism.  —  The  reactions  of  the  crayfish  to  food  are 
due  in  part  to  a  chemical  sense,  and,  since  "  the  animals  react  to 
chemical  stimulation  on  any  part  of  the  body  ...  we  must 
assume  that  there  are  chemical  sense-organs  all  over  the  body." 
(Bell.)  The  anterior  appendages,  however,  are  the  most  sensi- 
JtixS^specially  the  outer  ramus  of  the  antennule.  Positive  re- 
actions result  from  the  application  of  food  substances.  For 
example,  if  meat  juice  is  placed  in  the  water  near  an  animal,  the 
antennae  move  slightly,  and  the  mouth  parts  perform  vigorous 
chewing  movements.  Acids,  salts,  sugar,  and  other  chemicals 
produce  a  sort  of  negative  reaction  indicated  by  scratching  the 
carapace,  rubbing  the  chelae,  or  pulling  at  the  part  stimulated. 


292  COLLEGE   ZOOLOGY 

Habit  Formation.  —  It  has  been  shown  by  certain  simple 
experiments  that  crayfishes  are  able  to  learn  habits  and  to  modify 
them.  They  learn  by  experience  and  modify  their  behavior  slowly 
or  quickly,  depending  upon  their  familiarity  wdth  the  situation. 
One  investigator  has  trained  them  to  come  to  him  for  food. 
(Holmes.) 

h.  Crustacea  in  General 

(i)  Distinguishing  Features.  —  The  Crustacea  (Lat.  crusta, 
skin)  are  arthropods  most  of  which  live  in  the  water  and  breathe 
by  means  of  gills.  The  body  is  divided  into  head,  thorax,  and 
abdomen,  or  the  head  and  thorax  may  be  fused,  forming  a  cephalo- 
thorax.  The  head  usually  consists  of  five  segments  fused  to- 
gether; it  bears  two  pairs  of  antennae  (feelers),  one  pair  of 
mandibles  (jaws),  and  two  pairs  of  maxillae.  The  thorax  bears 
a  variable  number  of  appendages,  some  of  which  are  usually 
locomotory.  The  abdominal  segments  are  generally  narrow 
and  more  mobile  than  those  of  the  head  and  thorax;  they  bear 
appendages  which  are  often  reduced  in  size. 

(2)  Classification  of  the  Crustacea.^  —  The  Crustacea  belong- 
ing to  Subclasses  I-IV  are  often  placed  in  one  group  and  called 
Entomostraca.  They  are  of  small  size,  with  a  variable  num- 
ber of  body  segments,  and  usually  no  gastric  mill  in  the  stomach. 
They  are  apparently  more  primitively  organized  than  the  mem- 
bers of  Subclass  V,  the  Malacostraca.  Certain  fossil  animals, 
called  Trilobites  (Fig.  209),  are  by  many  authorities  included 
with  the  Crustacea.  They  have  one  pair  of  antennae,  and  nu- 
merous body  segments,  all  of  which  bear  biramous  appendages. 

Subclass  I.  Branchiopoda.  —  Crustacea  with  an  elongated 
body,  usually  a  carapace  or  shell,  and  many  pairs  of  lobed, 
foliaceous  swimming  feet. 
Order  i.  Phyllopoda. — Branchiopoda  with  from  ten  to 
thirty  pairs  of  leaf-like,  swimming  feet.  Examples: 
Branchipus,  (Fig.  210,  A),  Artemia  (Fig.  210,  B). 

1  Somewhat  simplified  from  Caiman  in  Lankester's  Treatise  on  Zoology. 


PHYLUM  ARTHROPODA 


293 


Fig. 


209.  Fig.  210. 

Fig.  209.  —  Dorsal  surface  of  a  Trilobite,  Triarthrus  becki.  (From  Sedg- 
wick's Zoology,  after  Beecher.) 

Fig.  210.  —  Suborder  Phyllopoda.  A,  Branchipus  stagnalis,  fresh-water 
form;  B,  Artemia  salina,  salt-water  form  of  the  same  crustacean.  (From  Ver- 
wom,  after  Semper.) 


,ant.Z 


Fig.  212. 

Fig.  211.  —  Suborder  Cladocera.  Daphnia,  a  water-flea,  ant.i,  anten- 
nule;  ant.2,  antenna ;  br,  brain ;  br.p,  brood-pouch;  E,  eye;  d.gl,  digestive 
gland;  /,  swimming  feet;  ht,  heart;  sh.gl,  shell-gland.  (From  Parker  and 
Haswell,  after  Claus.) 

Fig.  212.— -Order  Ostracoda.  Cypris  Candida,  i,  anteunules;  2,  anten- 
nae; 3,  mandibles;  4,  ist  maxillae;  5,  2d  maxillae;  6,  ist  paii  of  legs;  7,  2d 
pair  of  legs;   8,  tail;  p,  eye.     (From  Shipley  and  MacBride,  after  Zenker.) 


294  COLLEGE  ZOOLOGY 

Order  2.  Cladocera.  —  Small  Branchiopoda  with  bodies 
usually  enclosed  in  a  bivalve  shell,  large  second  anten- 
nae used  in  swimming,  and  four  to  six  pairs  of  swimming 
feet.  Examples:  Daphnia  (Fig.  211),  Leptodora. 
Subclass  II.  Ostracoda.  —  Small,  laterally  compressed  Crus- 
tacea entirely  enclosed  in  a  bivalve  shell.  Usually  seven 
pairs  of  appendages.  Examples:  Cypris  (Fig.  212), 
Candona. 
Subclass  III.  Copepoda.  Elongated  Crustacea  with  bira- 
mous  swimming  feet,  without  shell,  and  without  ab- 
dominal appendages.  Examples:  Cyclops  (Fig.  213),  Can- 
thocamptus,  Diaptomus,  Argulus,  Sapphirina,  Achtheres. 
Subclass  IV.  Cirripedia.  —  Crustacea  usually  fixed  or  para- 
sitic, with  indistinctly  segmented  body  enclosed  in  a 
carapace.  Often  greatly  modified  because  of  fixed  or 
parasitic  habit.  Examples:  Lepas,  Balanus  (Fig.  214), 
Sacculina,  Peltogaster. 
Subclass  V.  Malacostraca.  —  Crustacea  usually  of  large 
size,  with  five  segments  in  the  head,  eight  in  the  thorax, 
and  six  in  the  abdomen,  and  with  a  gastric  mill  in  the 
stomach. 

Order  i.  Nebaliacea.  —  Small,  shrimp-like  Malacostraca 
with  head  and  middle  portion  of  body  enclosed  in  a 
bivalve  shell,  with  eight  thoracic  segments,  eight  abdom- 
inal segments,  and  a  terminal  caudal  fork.  Example: 
Nebalia  (Fig.  215). 

Order  2.  Anaspidacea.  —  Malacostraca  with  distinct 
thoracic  segments,  pedunculate  eyes,  and  no  carapace. 
Example:   Anaspides. 

Order  3.  Mysidacea.  —  Malacostraca  of  small  size,  with 
biramous  antennules,  thoracic  limbs  with  natatory  exopo- 
dites,  and  a  large  carapace.     Example:  My  sis  (Fig.  217). 

Order  4.  Cumacea.  —  Malacostraca  with  a  slender  ab- 
domen, four  or  five  free  thoracic  segments,  and  a  small 
carapace.     Example:  Diastylis  (Fig.  218). 


PHYLUM  ARTHROPODA 


29s 


Fig.  213. 

Fig.  213.  —  Order  Copepoda.  Cyclops,  dorsal  view  of  female,  i,  ist 
antenna;  2,  2d  antenna;  3,  eye;  4,  ovary;  5,  uterus;  6,  oviduct;  7,  sperma- 
theca;  8,  egg-sacs;  0,  caudal  fork;  10,  position  of  anus;  11,  segment  consist- 
ing of  last  thoracic  and  first  abdominal.  (From  Shipley  and  MacBride,  partly 
after  Hartog.) 

Fig.  214.  —  Order  Cirripedia.  Balanus  tintinnabulum,  one-half  of  shell 
has  been  removed.  Ad,  adductor  muscle;  Od,  oviduct;  Oe,  opening  of  oviduct; 
Ov,  ovary;  Sc,  scutum;  Te,  tergum;  Tu,  section  of  outer  shell.  (From  Sedg- 
wick's Zoology,  after  Claus.) 


Fig.  215.  —  Order  Nebaliacea.  Nehalia  geoffroyi,  female.  A',  anten- 
nule;  A",  antenna;  D,  intestine;  M,  crop;  O,  stalked  eye;  R,  movable 
head  plate.     (From  Sedgwick's  Zoology,  after  Claus.) 


296 


COLLEGE  ZOOLOGY 


Fig.  2i6.  —  Order  Amphipoda.  Talorchestia  megalophthalniia.  (From  Paul- 
mier.) 

Fig.  217.  —  Order  Mysidacea.  Mysis  stenolepis.  (From  Paulmier,  after 
VerriU.) 


Fig.  2x8.  ^  Order  Cum  ace  a.     Diastylis  quadrispinosa.     (From  Paulmier, 
after  Verrill.) 


^<$j'~^^ 


Fig.  2ig.  —  Order  Tanaidacea.     Apseudes  spinosus.     (From  Sedgwick's 
Zoology,  after  Sars.) 


Fig.   220.  —  Order    Isopoda.     A,    Asellus    communis,    a    fresh-water    species., 
B,  Oniscus  asellus,  a  terrestrial  species.     (From  Paulmier;   A,  after  Smith.) 


PHYLUM   ARTHROPODA 


297 


Order  5.  Tanaidacea.  —  Malacostraca  with  free  thoracic 
segments  except  the  first  two,  which  are  fused  with  the 
head  and  extend  on  the  sides,  forming  a  respiratory- 
chamber.     Example:  Apseudes  (Fig.  219). 

Order  6.  Isopoda.  —  Malacostraca  with  a  body  generally 
broad  and  flat,  seven  free  thoracic  segments,  leaf-hke 
legs,  and  no  carapace.  Examples:  Asellus  (Fig.  220,  A), 
Armadillium,  Oniscus  (Fig.  220,  B),  Porcellio. 

Order  7.  Amphipoda.  —  Malacostraca  laterally  com- 
pressed, with  elongated  abdomen  bearing  three  pairs 
of  posteriorly  directed  springing  feet  and  three  pairs  of 
anterior  swimming  feet,  and  without  a  carapace.  Exam- 
ples: Gammarus  (Fig.  221,  A),  Talorchestia  (Fig.  216), 
Caprella  (Fig.  221,  B). 

Order  8.  Euphausiacea.  — Malacostraca  with  all  thoracic 
segments  covered  by  carapace,  pedunculate  eyes,  none 
of  thoracic  limbs  specialized  as  maxillipeds,  and  only 
podobranchiae  present.     Example:    Meganyctiphanes. 

Order  9.  Decapoda.  —  Malacostraca  wath  first  three  pairs 
of  thoracic  limbs  speciaUzed  as  maxilUpeds,  with  five 
pairs  of  thoracic  walking  legs,  with  generally  all  of  the 
thoracic  segments  covered  by  a  carapace,  and  with 
stalked,  compound  eyes. 
Suborder  i.  Natantia. — Decapoda  with  body  usually 
laterally  compressed,  legs  generally  slender,  and  pleopods 
always  present  in  full  number,  well  developed,  and  used 
for  swimming.  Examples:  PencEus,  Alpheus,  Falcemonetes 
(Fig.  224),  Stenopus. 
Suborder  2.  Reptantia.  —  Decapoda  with  body  not  com- 
pressed, legs  strong,  pleopods  often  reduced  or  absent, 
not  used  for  swimming.  Examples:  Hyas,  Cancer,  Cal- 
linectes  (Fig.  223),  Pinnotheres,  Cambarus  (Fig.  202), 
Homarus,  Palinurus,  Eupagurus,  Gelasimus  (Fig.  223,  B). 

Order  10.  Stomatopodk.  —  Malacostraca  with  five  pairs 
of  anterior  maxillipeds  on  the  thorax,  and  three  pairs  of 


298 


COLLEGE  ZOOLOGY 


Fig.  221.  —  Order  Amphipoda.     A,  Gammarus  fasciatus,  a  fresh-water  species. 
B,  Caprella  geomeirica,  a  marine  species.     (From  Paulmier.) 


B 

Fig.  222.  Fig.  223. 

Fig.  222.  —  Order  Stomatopoda.  Squilla  empusa,  the  mantis  shrimp. 
(From  Davenport,  after  Rathbun.)  •'• 

Fig.  223.  —  Order  Decapoda.  A,  Callinectes  hastatus,  edible  or  blue  crab. 
(From  Paulmier,  after  Rathbun.)  B,  Gelasimus  minax,  fiddler  or  soldier 
crab.     (From  Paulmier.) 


PHYLUM  ARTHROPOD  A  299 

thoracic,  biramous  legs,  with  caudal  fin,  and  short  cara- 
pace covering  only  part  of  the  thorax.     Examples :  Squilla 
(Fig.  222),  Gonodactylus. 
(3)  Entomostraca.  —  The   Crustacea  belonging  to  the  En- 
TOMOSTRACA  are  the  Branchiop^da,  Ostracoda,  Copepoda, 
and  CiRRiPEDiA.     They  live  in  fresh  water,  in  salt  water,  on 
land,  or  as  parasites  on  other  animals.     The  enormous  numbers 
of  these  little  creatures  may  be  ascertained  by  coimting  the 
specimens  that  are  captured  if  a  fine  gauze  net  is  drawn  through 
the  waters  of  lakes  or  streams.     It  has  been  estimated  that,  on 
the  average,  each  cubic  meter  of  water  in  the  small  Wisconsin 


Fig.  224.  —  Order  Decapoda.     P alcemonetes  vulgaris,  a  shrimp.     (From 
Davenport.) 

lakes  contains  about  40,000  individuals,  and  that  160  billion, 
weighing  altogether  about  twenty  tons,  may  exist  at  one  time  in 
a  lake  of  eighty  square  kilometers.  Usually  a  lesser  number  are 
present  in  the  waters  of  streams.  The  ocean  is  likewise  popu- 
lated with  bilHons  of  these  minute  Crustacea. 

These  small  Crustacea  are  of  little  if  any  direct  economic 
importance  to  man,  but  indirectly  they  are  of  considerable  value, 
since  they  form  the  chief  food  of  many  edible  fishes. 

The  Trilobita  are  extinct  Crustacea  which  are  known  only 
from  their  fossil  remains.  They  are  associated  in  the  strata  of 
the  earth's  crust  with  the  remains  of  Crinoidea  (Fig.  148), 
Brachiopoda  (Fig.  126),  and  Cephalopoda  (Fig.  191).  The 
best-known  species,  Triarthrus  hecki  (Fig.  209) ,  is  from  the  Utica 
shales  (Lower  Silurian)  of  New  York  State.  It  has  two  anten- 
nae and  many  biramous  appendages. 

The  Branchiopoda  include  the  leaf-legged  Crustacea  (Phyl- 
lopoda),  and  the  water- fleas  (Cladocera).     The  fairy-shrimp, 


300  COLLEGE  ZOOLOGY 

Branchipus  (Fig.  210,  A),  is  a  common  fresh-water  phyllopod; 
Artemia  (Fig.  210,  B)  is  a  genus  found  in  salt-water  lakes,  such 
as  the  Great  Salt  Lake  of  Utah.  Daphnia  (Fig.  211)  is  a  water- 
flea  (Cladocera)  abundant  in  fresh-water  ponds  and  lakes. 
Its  body  is  enclosed  in  a  shell,  and  the  second  antennae  {ant.  2) 
are  modified  to  form  swimming  appendages.  During  the  spring 
and  summer  only  females  are  present,  and  at  this  time  "  sum- 
mer "  eggs  are  produced  which  develop  parthenogenetically  in 
the  brood-pouch  {br.p)  of  the  mother.  In  the  autumn  males 
are  developed;  they  fertiUze  the  "winter"  eggs,  which  are 
larger  and  fewer  in  number  than  the  summer  eggs. 

The  OsTRACODA  (Fig.  212)  are  bivalved  Crustacea  which 
protrude  their  antennae  (2)  from  the  two  valves  of  their  shell  and 
use  them  as  oars  in  swimming.  They  are  common  in  ponds  and 
Streams. 

A  well-known  fresh- water  Copepod  is  Cyclops  (Fig.  213),  a 
species  that  has  a  single  compound  eye  {e)  in  the  middle  of  the 
head.  The  antennae  (j)  are  used  for  locomotion.  The  fe- 
male may  be  recognized  easily  during  the  summer  because  of  the 
two  brood  sacs  {8)  full  of  eggs  that  she  carries  about  with  her. 

The  subclass  Cirripedia  contains  the  barnacles  (Fig.  214). 
These  are  sessile  Crustacea,  many  of  which  possess  shells  caus- 
ing them  to  resemble  mollusks.  The  larvae  are  free  swimming 
and  resemble  those  of  other  Crustacea,  but  they  pass  through 
a  metamorphosis,  during  which  some  or  all  of  the  appendages 
and  other  parts  of  thebody  are  lost,  and  usually  a  calcareous  shell 
is  formed.  The  rock-barnacle,  Balanus  halanoides  (Fig.  214) 
is  abundant  along  the  North  Atlantic  coast,  where  it  lives  at- 
tached to  rocks  and  other  objects.  The  movements  of  the  ap- 
pendages create  a  current  of  water  which  brings  food  into  the  shell. 
The  goose  barnacle,  Lepas,  has  a  bivalve  shell  and  is  attached  by 
a  peduncle.  Sacculina  is  a  barnacle  parasitic  on  the  crab,  Car- 
cinus,  and  in  the  adult  stage  resembles  a  tumor,  consisting  almost 
entirely  of  reproductive  organs.  Most  barnacles  are  herm- 
aphroditic. 


PHYLUM   ARTHROPODA  301 

(4)  Malacostraca.  —  The  Malacostraca  are,  as  a  rule, 
larger  than  the  Entomostraca,  and  include  the  more  familiar 
Crustacea,  such  as  crayfishes,  lobsters,  crabs,  shrimps,  and 
sow-bugs.  Some  of  them  are  aquatic,  others  are  terrestrial, 
and  a  few  are  parasitic.  > 

The  order  Isopoda  contains  a  number  of  common  Malacos- 
traca (Fig.  220).  Most  of  them  are  marine,  but  some  live  in 
fresh  water  and  on  land.  They  are  the  largest  group  of  terres- 
trial Crustacea.  The  sow-bug,  Oniscus,  and  the  pill-bug,  Arma- 
dillium,  live  under  stones,  boards,  and  similar  places  that  are 
dark  and  moist.  Although  land  animals,  they  breathe  by  means 
of  gills  situated  on  the  under  surface  of  the  abdomen. 

The  Amphipoda  are  aquatic,  except  a  few  species  which  leap 
about  on  the  beach,  and  are  called  beach- fleas.  Gammarus 
(Fig.  221)  is  called  the  fresh- water  shrimp.  Talorchestia 
(Fig.  216)  is  a  sand-hopper  common  on  sandy  beaches  between 
the  tide-marks.  Caprella  is  a  peculiar  brown  amphipod  which 
so  closely  resembles  the  seaweeds  or  hydroids  among  which  it 
lives  that  it  can  be  detected  only  by  an  experienced  eye. 

The  mantis  shrimps  belong  to  the  order  Stomatopoda.  This 
common  name  was  derived  from  their  resemblance  to  the  insect 
called  the  praying-mantis  (Fig.  270).  They  are  exclusively 
marine.  Squilla  empusa  (Fig.  222)  lives  along  the  eastern  coast 
of  the  United  States. 

The  order  Decapoda  contains  the  lobsters,  crayfishes,  crabs, 
and  shrimps,  and  is  the  most  important  group  of  the  Crustacea. 
The  name  Decapoda  refers  to  the  fact  that  only  the  last  five 
pairs  of  thoracic  appendages  are  used  for  locomotion. 

The  lobster  is  of  considerable  economic  importance.  It  is 
most  abundant  along  the  Atlantic  coast  from  Labrador  to  Dela- 
ware Bay,  and  lives  on  the  bottom  from  near  shore  to  a  depth 
of  one  hundred  fathoms.  About  fifteen  million  lobsters  are  sent 
to  market  annually,  and  unless  their  capture  is  regulated,  they 
will  soon  be  exterminated.  Shrimps  and  prawns  are  also  used 
as  food  for  man.      Palcemoneles  (Fig.  224)  is  a  common  shrimp 


302 


COLLEGE  ZOOLOGY 


living  among  seaweeds;  it  is  almost  transparent.  The  hermit- 
crab,  Eupagurus,  lives  in  an  empty  snail-shell  which  protects  it 
from  many  enemies.  Some  hermit-crabs  place  sea-anemones 
or  hydroid  colonies  upon  their  shells;  these  furnish  additional 
protection. 

The  edible  or  blue  crab,  Callinectes,  lives  along  the  Atlantic 
and  Gulf  coasts  and  is  captured  in  large  numbers  for  market. 
It  is  called  the  soft-shelled  crab  just  after  molting.  The  fid- 
dler-crabs, Uca  pugilator,  are  common  along  our  eastern  coast, 
where  they  dig  holes  in  the  mud  and  sand.  The  spider-crab, 
Libinia,  has  long  slender  legs,  which  enable  it  to  run  over  uneven 
surfaces  with  ease.  The  Japanese  spider-crab  is  very  large, 
sometimes  measuring  twenty  feet  across  from  tip  to  tip  of  the 
first  pair  of  legs. 

(5)  The  Biogenetic  Law.  —  Early  in  the  past  century  it  was 
noticed  that  animals  could  be  arranged  in  a  series  beginning  with 
the  Protozoa  and  passing  through  the  simpler  diploblastic  forms, 
and  that  the  stages  in  this  series  correspond  to  the  early  stages 
in  the  embryology  of  the  M^tazoa.  This  led  to  the  formulation 
of  the  biogenetic  law,  i.e.  that  the  4ev^l9pffle^t  ftf  fe  ifi^iyidu^l 
recapitulates  the  stages  in  the  evolution  of  the  race,  or  ontogeny 
recapitulates  phytogeny.  These  stages  contrasted  appear  as 
follows:  — 

Phylogenetic  Stage  Ontogenetic  Stage 

(i)  Single-celled  animal  Egg  cell 

(2)  Ball  of  cells  Blastula 

(3)  Two-layered  sac  Gastrula 

(4)  Triploblastic  animal  Three-layered  embryo 

Zoologists  soon  became  interested  in  the  recapitulation  theory, 
and  enlarged  upon  it.  Of  these,  Fritz  Miiller  and  Ernst  Haeckel 
are  especially  worthy  of  mention.  The  latter  expressed  the  facts 
as  he  saw  them  in  his  "  fundamental  law  of  biogenesis."  The 
ancestor  of  the  many-celled  animals  was  conceived  by  him  as 


PHYLUM   ARTHROPODA 


303 


Fig. 


225.  ^ —  Larva  of  lobster  in  My  sis  stage. 
(From  Sedgwick,  after  Sars.) 


a  two-layered  sac 
something  like  a 
gastrula,  which  he 
called  a  Gastrcea. 
The  coelenterates 
were  considered  to 
be  gastriea  slightly 
modified. 

Fritz    Miiller    de- 
rived strong  arguments  in  favor  of  biogenesis  from  a  study  of 
certain   Crustacea  belonging  to  the  Malacostraca.     Many 
members  of  this  group  do 
not  emerge  from  the  egg 
so  nearly  Uke  the  adult  as 
does    the    crayfish.      The 
lobster,  for  example,  upon 
hatching     (Fig.     225)     re- 
sembles a  less  specialized 


Fig.  226.  —  Two  stages  in  the  development  of  the  shrimp,  Penceus. 
A,  Nauplius  stage.  B,  Protozocea  stage.  (From  Sedgwick's  Zoology,  after 
Fritz  Miiller.) 


304 


COLLEGE  ZOOLOGY 


prawnlike  crustacean  called  My  sis  (Fig.  217),  and  is  said  to  be 
in  the  Mysis  stage. 

The  shrimp,  PencBus,  passes  through  a  number  of  interesting 
stages  before  the  adult  condition  is  attained.     It  hatches  as  a 


Fig.  227.  —  Two  later  stages  in  the  development  of  Pejiceus.    A,  Zocea 
stage.     B,  Mysis  stage.     (From  Korschelt  and  Heider,  after  Claus.) 


larva,  termed  a  Nauplius  (Fig.  226,  A),  possessing  a  frontal  eye 
and  three  pairs  of  appendages  {A',  A",  Mdf.);  this  Nauplius 
molts  and  grows  into  a  Frotozocea  stage  (Fig.  226,  B),  which  bears 
three  more  pairs  of  appendages  and  the  rudiments  of  segments 
III-VIII.     The   Frotozocea  stage  grows  into   the  Zoeea  stage 


PHYLUAI   ARTHROPODA  305 

(Fig.  227,  A).  The  cephalo thorax  and  abdomen  are  distinct  at 
this  time;  eight  pairs  of  appendages  are  present  (I-VIII)  and 
six  more  are  developing  (ai-ae).  The  Zo(Ea  grows  and  molts  and 
becomes  a  My  sis  (Fig.  227,  B)  with  thirteen  pairs  of  appendages 
(I-VIII)  on  the  cephalothorax.  Binally,  the  Mysis  passes  into 
the  adult  shrimp,  which  possesses  the  characteristic  number  of 
appendages  (I- XIX),  each  modified  to  perform  its  particular 
function.  The  Nauplius  of  Penceus  resembles  the  larvae  of 
many  simple  crustaceans;  the  ZocBa  is  somewhat  similar  to  the 
condition  of  an  adult  Cyclops  (Fig.  213);  the  Mysis  is  like  the 
adult  Mysis  (Fig.  217);  and  finally  the  adult  Penceus  is  vaoxQ 
specialized  than  any  of  its  larval  stages,  and  belongs  among  the 
higher  Crustacea.  The  above  facts  have  convinced  some 
zoologists  that  Penceus  recapitulates  in  its  larval  development 
the  progress  of  the  race;  that  the  lobster  has  lost  many  of  these 
stages,  retaining  only  the  Mysds;  and  that  the  crayfish  hatches 
in  practically  the  adult  condition.  The  Nauplius  stage  of  the 
latter  is  supposed  to  be  represented  by  a  certain  embryonic 
phase  (Fig.  207,  B). 

The  law  of  biogenesis  has  been  criticized  severely  by  many 
prominent  zoologists,  but  it  has  furnished  an  hypothesis,  which 
has  concentrated  the  attention  of  scientists  upon  fundamental 
embryological  processes,  and  has,  therefore,  had  a  great  influence 
upon  zoological  progress. 

3.  Class  II.    Onychophora 

This  class  (Gr.  onux,  a  claw;  phoreo,  I  bear)  contains  about 
fifty  species  of  a  peculiar  arthropod,  usually  placed  in  a  single 
genus,  Peripatus  (Fig.  228),  but  probably  belonging  to  a  number 
of  genera.  Peripatus  has  been  reported  from  isolated  regions 
in  Africa,  Australia,  New  Zealand,  Tasmania,  New  Britain, 
Mexico,  South  America,  West  Indies,  and  Malaya,  and  is,  there- 
fore, an  excellent  example  of  an  animal  with  a  discontinuous 
distribution.  It  lives  in  crevices  of  rock,  under  bark  and  stones, 
and  in  other  dark  places.     As  the  animal  moves  slowly  from 

X 


3o6 


COLLEGE  ZOOLOGY 


place  to  place  by  means  of  its  legs,  the  two  extremely  sensitive 
antennae  test  the  ground  over  which  it  is  to  travel,  while  the  eyes, 
one  at  the  base  of  each  antenna,  enable  it  to  avoid  the  light. 


Fig.  228.  —  Peripatus  capensis,  drawn  from  life.     (From  Sedgwick.) 

When  irritated,  Peripatus  often  ejects  slime,  sometimes  to  the 
distance  of  almost  a  foot,  from  a  pair  of  glands  which  open  on  the 
oral  papillae.    This  slime  sticks  to  everything  but  the  body  of  the 

animal  itself;  it  is  used  principally 
to  capture  flies,  wood-lice,  termites, 
and  other  small  animals,  and  in 
addition  is  probably  a  weapon  of 
defense.  A  pair  of  modified  ap- 
pendages serve  as  jaws  and  tear  the 
food  to  pieces. 

Most    species  .of    Peripatus    are 
viviparous,  and  a  single  large  female 
may  produce  thirty  or  forty  young 
in  a  year.     These  young  resemble 
Fig.    229.  —  Peripatus    ca-   the    adults    when    born,    differing 

Pensts,    ventral   view   of   head.       ,  .    ^       • 

ant,    antenna;     F.l,    first    leg;    chiefly   m   Size   and   Color. 

The  external  appearance  of  Peri- 
patus capensis  is  shown  in  Figures 
228  and  229.  Figure  230  shows  the  principal  internal  organs 
of  a  male  specimen.  The  head  bears  three  pairs  of  append- 
ages: (i)  the  antennce  (Fig.  229,  ant.),  (2)  the  oral  papillce  (or.p), 
and  (3)  the  jaws,  a  pair  of  simple  eyes,  and  a  ventrally  placed 


or.p,    oral    papillae;    T,  tongue. 
(From  Sedgwick.) 


PHYLUM   ARTHROPODA 


307 


mouth.  The  fleshy  legs  number  from  seventeen  pairs  to  over 
forty  pairs  in  different  species;  each  (Fig.  229,  FA)  bears  two 
claws.    The  anus  is  at  the  posterior  end;    the  genital  pore  is 


the  last  pair  of 

\    i 

cord; 
lands; 
Bride, 

legs;    and  a  ne- 

phridiopore     Ues 

Awmk/-'* 

at    the    base    of 

.!■"» 

each    leg.      The 

/fyM  H\wt' 

M^-l 

skin    is    covered 

i 

WJiM  ^v^* 

°.S  i!§ 

with    papillcB, 

1 

1  "g  6 

each    bearing    a 

§ 

the  int« 
eyes; 
jnital  0 
a.     -(Fr 

spine;  these  pa- 

M 

Al 

.J2 

pillae  are  especi- 

m 

Jb-^ 

T 

ally  numerous  on 

m 

MX 

4 

the  antennae,  lips, 
and  oral  papillae, 
and  are  probably  ^^^ 

Jji 

1  < 

4 

--6      \ 

1   ^ 

2  'g  s ": 

^    CO- 

^  1  ^"-s  " 

tactile  (Fig.  229). 

1 

< 

L~j 

fj 

The     digestive 

1/ 

< 

^-4 

p 

11 

IsS-E 

system  (Fig.  230, 

< 

1  ^«> 
> 

capensis,  1 

°,     I  St,     2d, 

iharynx;  <?, 
rged  crural 

8)  is  very  simple, 
consisting    of    a 

1  <: 

'?^ 

1 

muscular     phar- 

f> 

ynx,     a    short 
oesophagus,  a  long. 

W  ji  S'  'iEf 

■•a,  <r>  •« 

saccular  stomachy 

vV  1 «  ^kI/ 

•  •«    «    ca   h 

and  a  short  intes- 

tine.     The    pair 

0  rt  c  u:  "^ 

<->    ^    (D    m    t-i 

of  salivary  glands 

(11),  which  open 

into  the  mouth  cavity,  are 

modified  nephridia. 

The  heart  is 

the  only  blood-vessel; 

it  is 

a   dorsal  tube 

with 

paired  ostia 

connecting  it  with  the 

pericardial  cavity  in 

which  it  lies.     The 

body-cavity  is  a  blood 

space 

i.e 

.  a  ha 

smocoel.     The  breathing 

3o8 


COLLEGE  ZOOLOGY 


organs  are  air-tubes,  called  trachece,  which  open  by  means  of 
pores  on  various  parts  of  the  body.  The  excretory  organs  are 
nephridia  {14),  one  at  the  base  of  each  leg.  The  vesicular  end 
of  the  nephridium  is  part  of  the  coelom.  The  nervous  system 
consists  of  a  brain  {4) ,  dorsally  situated  in  the  head,  and  a  pair 
of  ventral  nerve-cords  (6),  which  are  connected  by  many  trans- 
verse nerves.  The  sexes  are  separate,  and  the  cavities  of  the 
reproductive  organs  are  ccelomic. 

Peripatus  is  of  special  interest  since  its  body  exhibits  certain 
structures  characteristic  of  annelids  and  other  structures  found 
only  in  arthropods.  It  is,  however,  undoubtedly  an  arthropod. 
The  following  table  (XI)  presents  briefly  these  characteristics 
and  shows  in  what  respects  it  differs  from  other  arthropods :  — 

TABLE  XI 

THE  CHARACTERISTICS  OF  PERIPATUS  ARRANGED  SO  AS  TO  SHOW  THE 
SIMILARITY   TO   AND   DIFFERENCES    FROM    ARTHROPODS   AND   ANNELIDS 


Arthropod 
Characteristics 


Appendages  modi- 
fied as  jaws. 

A  haemocoelic  body- 
cavity. 

No  coelom  around 
alimentary  canal. 

Tracheae  present. 


Annelid  Characteristics 


Paired  segmentally  ar- 
ranged nephridia. 

Cilia  in  reproductive 
organs. 

Chief  systems  of  organs 
arranged  as  in  anne- 
Hds. 


Structures  Peculiar  to 
Peripatus 


Number  and  diffusion 
of  tracheal  apertures. 
Single  pair  of  jaws. 
Distribution  of  repro- 
ductive organs. 
Texture  of  skin. 
Simplicity    and    simi- 
larity of  segments  be- 
hind the  head. 


4.   Class  III.    Myriapoda 

The  Myriapoda  (Gr.  murios,  ten  thousand;  podes,  feet)  are 
terrestrial  arthropods  commonly  known  as  centipedes,  or  wire- 
worms.  They  do  not  constitute  a  compact  group  of  animals, 
and  authorities  differ  with  regard  to  their  classification.     The 


PHYLUM  ARTHROPODA 


309 


four  orders  adopted  in  this  book  are  ranked  as  phyla  by  some 
zoologists.  The  chief  distinguishing  characteristics^  of  the  group 
are:  (i)  a  distinct  head  with  one  pair  of  tentacles  and  one  pair  of 
mandibles,  (2)  numerous  body  segments  bear- 
ing similar  leglike  appendages,  (^\  tracheae 
with  segmentally  arranged  apertures,  and 
(4)  excretory  organs  (malpighian  tubules) 
opening  into  the  intestine. 

Order  i .  Pauropoda  (Fig.  231).  —  These 
are  small  myriopods  less  than  2  mm.  in 
length  which  prey  on  microscopic  animals 
or  eat  decaying  animal  and  vegetable 
matter.  They  are  without  eyes,  heart,  and 
special  respiratory  organs,  and  evidently 
breathe  through  the  general  surface  of  the 
body,  as  in  the  earthworm.  The  head  is 
distinct,  and  the  body  contains  twelve  seg- 
ments and  bears  nine  pairs  of  legs.  The 
Pauropoda  are  apparently  primitive  myrio- 
pods related  to  the  millipedes  (Diplopoda). 
Pauropus  and  Eurypauropus  are  North  American  genera. 

Order  2.  Diplopoda.  —  The  Diplopoda  are  called  millipedes 
(Fig.  232).  The  body  is  subcylindrical,  and  consists  of  from 
about  twenty-five  to  more  than  one  hundred  segments,  accord- 


FiG.  231.  —  Order 
Pauropoda.  Pauropus 
huxleyi.  (From  Sedg- 
wick's Zoology,  after 
Latzel.) 


Fig.  232.  —  A  millipede.     (From  Shipley  and  MacBride,  after  Koch.) 


ing  to  the  species.  Almost  every  segment  bears  two  pairs  of 
appendages  (Fig.  232,  3),  and  has  probably  arisen  by -the  fusion 
of  two  segments.     The  mouth  parts  are  a  pair  of  mandibles  and 


3IO 


COLLEGE  ZOOLOGY 


a  pair  of  maxillce.  One  pair  of  antennce  (i)  and  either  simple  or 
aggregated  eyes  (2)  are  usually  present.  There  are  olfactory 
hairs  on  the  antennae  and  a  pair  of  scent  glands  in  each  segment, 
opening  laterally  (4).  The  breathing  tubes  (tracheae)  are  usually 
unbranched;  they  arise  in  tufts  from  pouches  which  open  just 
in  front  of  the  legs.  The  heart  is  a  dorsal  vessel  with  lateral  ostia; 
it  gives  rise  to  arteries  in  the  head.  The  two  or  four  excretory 
organs  are  thread-like  tubes  (malpighian  tubules)  which  pour 
their  excretions  into  the  intestine. 

The  millipedes  move  very  slowly  in  spite  of  their  numerous 
legs.     Some  of  them  are  able  to  roll  themselves  into  a  spiral  or 

ball.  They  live  in  dark,  moist  places 
and  feed  principally  on  vegetable  sub- 
stances. The  sexes  are  separate,  and 
the  eggs  are  laid  in  damp  earth.  The 
young  have  few  segments  and  only 
three  pairs  of  legs  when  they  hatch, 
and  resemble  apterous  insects  (Fig. 
259).  Other  segments  are  added  just 
in  front  of  the  anal  segment.  Ex- 
amples: Julus  (Fig.  232),  Polydesmus, 
Spiroholus. 

Order  3.   Chilopoda.  — The  Chilop- 

ODA  are  called  centipedes  (Fig.  233). 

The  body  is  flattened  dorso-ventrally, 

and  consists  of  from  fifteen  to  over 

one  hundred  and  fifty  segments,  each 

of  which  bears  one  pair  of  legs  except 

the  last  two  and  the  one  just  back  of 

the  head.     The  latter  bears  a  pair  of 

poison   claws    (Fig.   233,    Kf)    called   maxillipeds,   with   which 

insects,  worms,  moUusks,  and  other  small  animals  are  killed  for 

food. 

The  internal  anatomy  of  a  common  centiped  is  shown  in  Figure 
234.     The  alimentary  canal  (11)  is  simple;  into  it  opens  the  ex- 


FiG.  233.  —  A  centipede, 
Lithobiusjorficatus.  Kf,  poison 
claws.  (From  Sedgwick's 
Zoology,  after  Koch.) 


PHYLUM   ARTHROPODA 


311 


cretory  organs  —  two  malpighian  tubules  (6).  The  trachece  are 
branched,  and  open  by  a  pair  of  stigmata  in  almost  every  seg- 
ment. The  reproductive  organs  (10)  are  connected  with  several 
accessory  glands  (8).  Eggs  are  usually 
laid.  Those  of  Lithohius  are  laic^  singly 
and  covered  with  earth. 

The  centipedes  are  swift-moving  crea- 
tures. Many  of  them  live  under  the  bark 
of  logs,  or  under  stones.  The  genera 
Lithobius,  Geophilus,  and  Scutigera  are 
common.  The  poisonous  centipedes  of 
tropical  countries  belong  to  the  genus 
Scolopendra.  They  may  reach  a  foot  in 
length,  and  their  bite  is  painful  and  even 
dangerous  to  man. 

Order  4.  Symphyla.  —  The  Symphyla 
are  small  myriopods 
with  twelve  pairs  of 
legs.  The  head  bears 
antennae,  mandibles, 
maxillulae,  maxillae, 
and  a  labium.  Only 
two  genera,  Scolopen- 
drella  and  Scutigerella 
(Fig.  235),  and  twenty- 
four  species  belong  to 
the  order.  They  re- 
semble certain  wing- 
less insects   (Aptera, 


Fig.   235. 
Symphyla. 


Fig.  259)  in  habits  and 

appearance,  but  have   f''^^^     immacuiata. 

(From    Sedgwick  s 
a    greater    number    of    Zoology,  after  Latzel.) 

legs.      They    live    in 

moist  places  and  avoid  the  light.     Their  food  probably  consists 

of  small  insects. 


Fig.  234.  —  A  centi- 
pede, Lithobius  forficatus, 
dissected  to  show  internal 
organs,  i,  antenna; 
2,  poison  claw;  3,  salivary 
gland  ;    4,  walking   legs ; 

5,  ventral      nerve-cord ; 

6,  malpighian      tubule  ; 

7,  seminal  vesicle;  8,  small 
accessory  gland;  9,  large 
accessory  gland;  10,  tes- 
tis; II,  alimentary  canal. 
(From  Shipley  and  Mac- 
Bride,  after  Vogt  and 
Yung.) 


312  COLLEGE   ZOOLOGY 

5.   Class  IV.    Insect  a 

a.  The  Honey-bee 

The  honey-bee,  Apis  meUifica,  is  one  of  the  most  interesting  of 
all  insects  (Lat.  insectus,  cut  into)  because  of  its  wonderful  adap- 
tations to  its  environment,  its  complex  social  life,  and  its  economic 
value  to  man.  Honey-bees  live  in  colonies  of  about  sixty  thou- 
sand, in  which  there  are  three  kinds  of  individuals  —  workers, 
drones,  and  a  queen.     The  queen  (Fig.  236)  normally  lays  all  the 


9  ^ 

9 

MALE  FEMALE  WORKER 

Fig.  236.  —  The  honey-bee,  Apis  mellifica.     (From  Shipley  and  MacBride.) 

eggs.  She  lives  for  three  years  or  more  and  can  be  distinguished 
from  the  other  bees  by  the  greater  length  of  her  abdomen  and 
the  absence  of  a  pollen  basket  (Fig.  238,  A,  H).  The  drone 
(Fig.  236)  is  the  male  bee;  he  does  no  work,  but  lives  only  to 
mate  with  the  queen.  His  abdomen  is  broad;  his  eyes  are  very 
large;  and  he  has  no  pollen  basket.  The  worker  (Fig.  236)  is  a 
sexually  undeveloped  female;  it  does  not  lay  eggs  normally,  but 
spends  its  time  caring  for  the  colony.  Unless  otherwise  stated, 
the  following  description_refers  to  the  worker  bee. 

Anatomy  and  Physiology.  —  External  Features.  —  The 
body  of  the  honey-bee  is  supported  and  protected  by  a  firm  exo- 
skeleton  of  chitin.  Three  regions  are  recognizable  —  the  head, 
thorax,  and  abdomen. 

The  head  (Fig.  237)  consists  of  probably  six  segments  fused 
together,  forming  a  skull.  On  either  side  is  a  large  compound  eye; 
on  top  are  three  simple  eyes  (ocelli) ;  in  front  are  tWo  antennce  (a) ; 
and  projecting  downward  are  a  number  of  mouth  parts. 


PmXUM   ARTHROPODA 


313 


The  mouth  parts  consist  of  a  labrum,  or  upper  lip,  the  epi- 
pharynx  (Fig.  237,  g),  a  pair  of  mandibles  (m),  two  maxillae  (mx), 
and  a  labium,  or  under  lip  {I,  Ip.).  The  labrum  is  joined  to  the 
clypeus,  which  lies  just  above  it.  From  beneath  the  labrum 
projects  the  fleshy  epi- 
pharynx  (g);  this  is  prob- 
ably an  organ  of  taste. 
The  mandibles,  or  jaws  (m), 
are  situated  one  on  either 
side  of  the  labrum;  they 
are  notched  in  the  queen 
and  drone,  but  smooth  in 
the  worker.  The  latter 
makes  use  of  them  in 
building  honeycomb.  The 
labium  is  a  complicated 
median  structure  extend- 
ing downward  from  be- 
neath the  labrum.  It  is 
joined  to  the  back  of  the 
head  by  a  triangular  piece, 
the"  submenturn.  Next  to 
this  is  a  chitinous,  muscle- 
filled  piece,  the  mentum, 
beyond  which  is  the  ligula, 
or  tongue  (/),  with  one 
labial  palpus  (Ip)  on  each 
side.  The  ligula  may  be 
drawn  in  or  extended.     It 

is  long  and  flexible,  w^ith  a  spoon  or  bouton  (b)  at  the  end.  Hairs 
of  various  kinds  are  arranged  upon  it  in  regular  rows;  these  are 
used  for  gathering  nectar,  and  as  organs  of  touch  and  taste. 
The  maxillce  (Fig.  2^j,mx),  or  lower  jaws,  fit  over  the  mentum 
on  either  side.  Along  their  front  edges  are  rows  of  stiff  hairs. 
Maxillary  palpi  (mxp)  are  also  present. 


Head   of  worker  honey-bee. 

b,    bouton  ;     g,    epipharynx ; 

mx,  maxilla;  mxp,  maxillary 
palpus;  /,  hypopharynx;  Ip,  labial  palpus. 
(From  Packard,  after  Cheshire.) 


Fig.  237. 
a,  antenna; 
m,  mandible 


314  COLLEGE  ZOOLOGY 

Nectar  is  collected  in  the  following  manner.  The  maxillae 
and  the  labial  palpi  form  a  tube,  in  the  center  of  which  the  tongue 
moves  backward  and  forward.  When  the  epipharynx  is  lowered, 
a  passage  is  completed  into  the  oesophagus.  The  nectar  is  first 
collected  by  the  hairs  on  the  ligula;  it  is  then  forced  upward 
by  the  pressing  together  of  the  maxillae  and  labial  palpi. 

The  thorax  consists  of  three  segments,  each  of  which  bears  a 
pair  of  legs.  The  anterior  segment  is  known  as  the  prothorax, 
the  middle  segment  as  the  mesothorax,  and  the  posterior  segment, 
as  the  metathorax  The  mesothorax  and  metathorax  each  sup- 
port a  pair  of  wings.  The  segments  of  the  thorax  are  compara- 
tively large,  since  they  contain  the  largest  and  most  important 
muscles  of  the  body.  Externally  the  thorax  is  covered  with 
flexible  branched  hairs,  which  are  of  use  in  gathering  pollen. 

Perhaps  the  most  interesting  structures  of  the  honey-bee  are 
the  legs  of  the  worker  (Fig.  238).  The  parts  of  a  typical  insect 
leg,  naming  them  in  order  beginning  at  the  proximal  end,  are 
tYitcoxa  (c),  trochanter  (tr),femur  (f),  tibia  (/f),and  five-jointed 
tarsus  (t). 

The  prothoracic  legs  (Fig.  283,  C)  possess  the  following  useful 
structures.  The  femur  (/)  and  the  tibia  (ti)  are  clothed  with 
branched  hairs  for  gathering  pollen.  Extending  on  one  side  from 
the  distal  end  of  the  tibia  are  a  number  of  curved  bristles,  the 
pollen  brush  {binC  and  E),  which  are  used  to  brush  up  the  pollen 
loosened  by  the  coarser  spines;  on  the  other  side  is  a  flattened 
movable  spine,  the  velum  {v  in  C  and  E),  which  fits  over  a  curved 
indentation  in  the  first  tarsal  joint  or  metatarsus  (p  in  C). 
This  entire  structure  is  called  the  anjenna  cleaner  and  the  row 
of  teeth  (F)  which  lines  the  indentation  is  known  as  the  antenna 
comb.  Figure  238,  H,  shows  in  section  how  the  antenna  (a) 
is  cleaned  by  being  pulled  between  the  teeth  (c)  on  the  meta- 
tarsus (0  and  the  edge  (s)  of  the  velum  (v).  On  the  front  of  the 
metatarsus  is  a  row  of  spines  (eb  in  C)  called  the  eye  brush, 
which  is  used  to  brush  out  any  pollen  or  foreign  particles  lodged 
among  the  hairs  on  the  compoimd  eyes.     The  last  tarsal  joint 


Fig.  238.  —  Legs  of  worker  honey-bee.  A,  outer  side  of  metathoracic  leg. 
p,  metatarsus;  /,  tarsus;  ti,  tibia.  B,  inner  side  of  metathoracic  leg.  c,  coxa; 
p,  metatarsus;  t,  tarsus;  ti,  tibia;  tr,  trochanter;  wp,  wax  pinchers.  C,  pro- 
thoracic  leg.  h,  pollen  brush;  eb,  eye  brush;  p,  metatarsus;  /,  tarsus;  ti,  tibia; 
V,  velum.  D,  mesothoracic.leg;  lettering  as  in  C.  s,  pollen  spur.  E,  joint  of 
prothoracic  leg;  lettering  as  in  C.  F,  teeth  of  antenna  comb.  G,  transverse 
section  of  tibia  through  pollen  basket,  fa,  pollen;  h,  holding  hairs;  n,  nerve. 
H,  antenna  in  process  of  cleaning,  a,  antenna;  c,  antenna  comb;  /,  section  of 
leg;  s,  scraping  edge  of  v,  velum.     (From  Root,  after  Cheshire.) 


3i6 


COLLEGE  ZOOLOGY 


of  every  leg  (Fig.  239)  bears  a  pair  of  notched  claws  (an)  which 
enable  the  bee  to  obtain  a  foothold  on  rough  surfaces.  Between 
the  claws  is  a  fleshy  glandular  lobule,  the  pulvillus  (pv),  whose 
sticky  secretion  makes  it  possible  for  the  bee  to  cling  to  smooth 
objects.     Tactile  hairs  are  also  present  (fh). 

The_ middle,  of  mesothoracic  le^s  (Fig.  238,  D),  are  provided 
with  a  pollen-brush  (b),  but,  instead  of  an  antenna  cleaner,  a 
spur  (s)  is  present  at  the  distal  end  of  the  tibia.  This  spur  is 
used  to  piy  the  pollen  out  of  the  pollen 
baskets  on  the  third  pair  of  legs,  and  to 
clean  the  wings. 

Xhe  metathoracic  legs  (Fig.  238,  A  and  B) 
possess  three  very  remarkable  structures, 
the  pollen  basket,  the  wax  pinchers  {wp 
in  B),  and  the  pollen  combs  (at  p  mB). 
The  pollen  basket  consists  of  a  concavity 
in  the  outer  surface  of  the  tibia  with  rows 
of  curved  bristles  along  the  edges  {timK). 
By  storing  pollen  in  this  basket-like  struc- 
ture, it  is  possible  for  the  bee  to  spend 
more  time  in  the  field,  and  to  carry  a 
larger  load  at  each  trip.  The  pollen 
basket  in  cross-section  is  shown  in 
Figure  238,  G.  The  pollen  combs  (at  p 
in  B)  serve  to  fill  the  basket  by  combing 
out  the  pollen,  which  has  become  entangled  in  the  hairs  on  the 
thorax,  and  transferring  it  to  the  concavity  in  the  tibia  of  the 
opposite  leg.  At  the  distal  end  of  the  tibia  is  a  row^  of  wide 
spines;  these  are  opposed  by  a  smooth  plate  on  the  proximal  end 
of  the  metatarsus.  The  term  wax  pinchers  (wi?  in  B)  has  been 
applied  to  these  structures,  since  they  are  used  to  remove  the 
wax  plates  from  the  abdomen  of  the  worker. 

The  wings  are  membranes  supported  by  hollow  ribs  called 
nerves  or  veins.  The  pair  of  wings  on  one  side  of  the  body  may 
be  joined  together  by  a  row  of  hooklets  on  the  anterior  margin  of 


Fig.  239.  —  Foot  of 
the  honey-bee.  an,  claw; 
fh,  tactile  hairs;  pv,  pul- 
villus; t,  tarsal  segments. 
(From  Packard,  after 
Cheshire.) 


PHYLmi   ARTHROPODA 


317 


the  hind  wing,  which  are  inserted  into  a  trough-hke  fold  in  the 
posterior  margin  of  the  fore  wing.  When  flying,  the  wings  act 
as  incHned  planes, 
and  locomotion  for- 
ward is  attained  by 
both  up  and  down 
strokes,  the  tips  of 
the  wings  moving  in 
a  curve  shaped  like 
a  figure  8.  Motion 
backward,  or  a  sud- 
den stop,  may  be 
accomplished  by 
changing  the  inclina- 
tion of  the  plane  of 
oscillation. 

The  abdomen  is 
made  up  of  a  series 
of  six  visible  seg- 
ments; thin,  chitin- 
ous  membranes  con- 
nect the  segments 
and  make  the  move- 
ment and  expansion 
of  the  abdomen  posr 
sible.  Each  of  the 
last  four  visible  seg- 
ments of  the  worker      ^  c-       ^       1      u        u        rut. 

Fig.   240.  —  Sting  of  worker  honey-bee.     0,  barbs 
bears   a   pair' of   wax    on  darts;    7.  )fe, /,  levers  to   move  darts;    n,   nerve*; 

Zlands.    At  the  end  of    ^;  '^!."S-/r^'' ;    ^^'  P^i^on  g^.^nd;    ^  poison  sac; 
^  sh,  sheath;   5th g,  fifth  abdominal  ganghon.     (From 

the  abdomen  of  the    Packard,  after  Cheshire.) 

worker  and  queen  is 

the  stin^,  and  the  slit-like  openings  of  the  sexual  organs  and  anus. 

There  is  no  sting  in  the  drone,  but  a  copulatory  organ  is  present. 

The  sting  is  a  very  complicated  structure  (Fig.  240).     Before 


3i8 


COLLEGE  ZOOLOGY 


the  bee  stings,  a  suitable  place  is  selected  with  the  help  of  the 

sting  feelers    (p) ;    then   the 
two  barbed  darts  (b)  are  thrust 
forward.      The    sheath    (sh) 
serves  to  guide  the  darts,  to 
open  up  the  wound,  and  to 
aid  in  conducting  the  poison. 
The  i)oison  is  secreted  in  a 
pair  of  glands  (pg),  one  acid, 
the    other    alkaline,    and    is 
stored    in    a    reservoir    (ps). 
Generally   the   sting,   poison 
glands,  and  part  of  the  in- 
testine are  pulled  out  when 
a  bee  stings,  so  that  death 
ensues  after  several  hours,  but 
if  only  the  sting  is  lost, 
the  bee  is  not  fatally  in- 
jured.   The  queen 
seldom    uses    her 
sting     except     in 
combat  with  other 
queens. 

The      Anatomy 

and       Physiology 

of     the     Internal     Organs.  — 

Digestion   (Fig.    241), — The 

mouth    opens    into    a    narrow 

(esophagus       {oe), 

Fig.   241. — Internal  organs  of  honey-bee.     ht,  mal-      rU'  y.       \      A        f 

pighian  tubules;   c.s,  true  stomach;   dv,  dorsal  vessel;  wnicn      leaos      tO 

«.  eye;      g,  ganglia   of    nerve   chain;     hs,  honey  sac;  Xhe  honey  SaC  Qis) , 
li,    rectum ;    Ip,    labial    palpus ;    mesa.t,    mesothorax ;      •.       .     i  ,  i 

meia.t,   metathorax;    mx,   maxilla;    n,   nerves;    No.   i,  Sltuatea   near   tne 

No.  2,  No.  3,  salivary  glands;  ae,  oesophagus;  p,  stomach  anterior      end      of 


mouth;    pro.t,  prothorax;   si,  small  intestine  (ileum); 


V,  ventricles  of    dorsal  vessel. 
Cheshire.) 


(From  Packard,  after 


the      abdomen. 
The     stomach 


PHYLUM   ARTHROPODA 


319 


TraSc 


mouth  (p),  with  its  four  triangular  lips,  regulates  the  passage  of 
the  pollen  or  honey  taken  in  as  food  into  the  true  stomach  (c.s). 
The  digestive  juices  se- 
creted by  the  walls  of  the 
true  stomach  change  the 
food  into  chyme.  Part 
of  the  chyme  is  absorbed; 
the  rest  of  the  food  ma- 
terial is  forced  by  mus- 
cular contractions  into 
the  small  intestine  (si), 
where  digestion  and  ab- 
sorption are  completed. 
Undigested  particles  pass 
into  the  rectum  (li)  and 
out  of  the  anus.  One 
pair  of  salivary  glands 
(No.  2)  lie  in  the  head,  a 
second  pair  (No.  3)  in  the 
thorax;  they  pour  alka- 
line secretions  upon  the 
food  as  it  is  taken  into 
the  oesophagus. 

Circulation.  —  The 
hlood  is  a  plasma  contain- 
ing ameboid  corpuscles, 
but  differs  from  that 
of  most  animals  since  it  ,  Fig  242.  -  Respiratory  system  of  worker 
honey-bee  as  seen  from  above,  one  anterior 
carries  very  little,  if  any,  pair  of  abdominal  sacs  removed  and  transverse 
oxygen.      The  dorsal  Ves-     yentral  commissures  of   abdomen  riot  shown. 

■^°  _  I  sp,  III  sp,  VII  sp,   spiracles;  HtTraSc,  Tra 

set  or  heart  (Fig.  241,  dv)     Sc,  i,  2,  4,  7,  8,  10,  tracheal  sacs;   Tra,  tracheae. 

is  the  principal  organ  of    '^:T^:^tTKj:t  '"'"  "'  ""■  ^^'" 
circulation.      Blood  en- 
ters it  through  five  pairs  of  lateral  ostia,  and  is  forced  forward  by 
rhythmical  contractions.     From  the  head  region  the  blood  finds 


HtTraSc 


320 


COLLEGE  ZOOLOGY 


its  way  through  spaces  (haemocoel)  to  the  ventral  part  of  the 
body,  and  thence  to  the  pericardial  sinus  just  beneath  the  heart. 
The  muscular  diaphragm  of  the  pericardial  sinus  forces  the  blood 
through  the  ostia  into  the  heart. 

Rf.sptt^atton  fFJg.  242). — The  honey-bee  breathes  through 
seven  pairs  of  lateral  openings  called  spiracles,  one  pair  in  the 
prothorax  {1  Sp),  one  in  the  metathorax  (/  Sp),  and  five  in 
the  abdomen  (///  Sp,  VII  Sp).  The  spiracles  open  into  tubes 
called  trachecB  (Tra)  which  branch  and 
carry  air  to  all  parts  of  the  body.  Cer- 
tain tracheae  are  dilated  to  form  air 
sacs  (TraSc),  which  are  supposed  to  be 
of  value  during  flight,  since  they  can  be 
enlarged  at  will  and  the  specific  gravity 
of  the  insect  correspondingly  decreased. 
Figure  243  shows  the  trachea  to  consist 
of  a  tube  of  a  single  layer  of  cells  (a) 
lined  with  chitin  which  .is  thickened 
so  as  to  form  a  spiral  thread.  This 
chitinous  lining  keeps  the  trachea  open. 
Each  spiracle  is  provided  with  a  valve 
which  helps  prevent  the  entrance 
of  dust.  Oxygen  is  carried  directly 
to  the  tissues  by  the  tracheae  and  does 
not  need  to  be  transported  by  the 
blood. 

ExcRETTON.  —  The  excretory  organs  are  long,  thread-like 
tubes  called  malpi^hian  tubules  (Fig.  241,  bt).  They  pour  their 
excretions  into  the  intestine  at  the  point  where  it  joins  the 
stomach. 

Nervous  System.  —  There  is  a  complicated  bilobed  ganglionic 
mass,  the  brain,  in  the  dorsal  part  of  the  head.  Nerves  connect 
the  brain  with  the  compound  eyes,  ocelli,  antennae  and  labrum. 
The  brain  is  connected  by  nerve-cords  with  the  sub  oesophageal 
ganglion  \yhich  lies  beneath  the  oesophagus  in  the  head.     This 


Fig.  243.  —  Portion  of  a 
trachea.  a,  cellular  wall ; 
b,  nuclei.  (From  Packard, 
after  Leydig.) 


PHYLUM   ARTHROPODA 


321 


ganglion  innervates  the  mandibles,  labium,  and  other  mouth 
parts.  From  the  sub  oesophageal  ganglion  a  ventral  chain  of 
ganglia  (Fig.  241,  g)  extends  posteriorly  through  the  thorax  and 
into  the  abdomen.  Small  stomato-gastric  ganglia  are  connected 
with  the  organs  of  digestion,  circulation,  and  respiration,  and  a 
delicate,  sympathetic  nervous  system  is  also  present. 

Sense  Organs. — The  compound  eyes  are  constructed  on  a 
plan  similar  to  those  of  the  crayfish  (p.  285,  Fig.  203)  and  are 
especially  adapted  for  seeing  moving  objects.  The  ocelli  are 
less  complex  than  the  compound  eyes,  and  are  probably  of  use 


Fig.  244.  —  Longitudinal  section  through  part  of  an  antenna  of  a  worker 
honey-bee.  c,  conoid  hairs ;  /,  tactile  hairs ;  ho,  auditory  pits ;  n,  nerves ; 
s,  smell  hollows.     (From  Cheshire.) 

• 

only  to  distinguish  light  from  darkness,  although  they  may  per- 
ceive form  at  very  short  distances. 

The  principal  organs  of  smell  are  situated  on  the  antennae. 
They  are  hollows  in  the  cuticle  ^Fig.  244,  5),  connected  with  a 
cell  supplied  with  nerve- fibers  {n).  The  queen  possesses  about 
1600  smell  hollows  on  each  antenna,  the  worker  2400,  and  the 
drone  37,800.  The  sense  of  smell  is  considered  of  great  impor- 
tance in  the  life  activities  of  bees. 

Pits  near  the  mouth  of  the  bee  have  been  identified  as  taste_ 
orzans.     Taste  setae  are  present  near  the  end  of  the  ligula  (Fig. 

237,  ^)- 

Certain  pits  on  the  antennae  are  supposed  to  be  end  organs 
of  hearing  (Fig.  244,  ho).     Soimds  are  produced   by  the  vibra- 


322 


COLLEGE  ZOOLOGY 


tions  of  the  wings  and  by  the  vibrations  of  a  membrane  which 
lies  within  each  spiracular  opening  of  the  respiratory  system. 

Sense-organs  of  touch  are  hair-like  structures  on  various  parts 
of  the  body,  but  especially  numerous  on  the  antennae.  Two 
kinds  are  shown  in  Fig.  244,  (i)  small  hairs  (/),  and  (2)  large 
"  conoid  "  hairs  {c). 

Reproduction.  — The  sexes  are  separate  except  in  abnormal 
cases.     The  spermatozoa  arise  in  the  two  testes  (Fig.  245,  Tes), 

and  pass  through  the  vasa 

res  ^ 


AcCl 


VDef 


deferentia  (VDef)  into  the 
seminal  vesicles  ( Ves) ,  where 
they  are  stored.  The  sem- 
inal vesicles  open  into  large 
mucous  glands  (AcGl)  which 
unite  at  a  point  where  the 
ejaculatory  duct  begins  ( EjD). 
During  mating  the  sperma- 
tozoa pass  through  the 
ejaculatory  duct  and  are 
transferred  to  the  seminal 
receptacle  of  the  female 
(Fig.  246,  Spm)  by  the 
penis  (Fig.  245,  Fen). 

The  reproductive  organs 
of  the  workers  are  undevel- 
oped ovaries.  The  abdomen  of  the  queen  is  almost  completely 
filled  by  the  two  ovaries  (Fig.  246,  Ov). .  Each  ovary  consists  of 
a  number  of  ovarian  tubules  (ov)  in  which  are  eggs  in  various 
stages  of  development.  When  ready  for  deposition,  the  eggs  pass 
through  the  oviducts  (OvD)  into  the  vagina  (  Vag).  They  are 
fertilized  by  spermatozoa  from  the  seminal  receptacle  (Spm)  or 
spermatheca.  The  queen  seems  to  be  able  to  lay  fertihzed  or 
unfertilized  eggs  according  to  the  size  of  the  cell  in  which  they 
are  to  develop.  Fertilized  eggs  are  laid  either  in  small  worker 
cells  (Fig.  248)  or  in  large  irregular  queen  cells,  and  develop  into 


Fig.  245.  —  Reproductive  organs  of  drone 
bee,  dorsal  view,  natural  position.  A  cGl,  ac- 
cessory gland;  B,  bulb  of  penis;  EjD,  ejac- 
ulatory duct;  Pen,  penis;  Tes,  testis; 
vDef,  vas  deferens;  Ves,  seminal  vesicle; 
//,  uu,  yy,  zz,  parts  of  penis.  (From  Snod- 
grass.  Tech.  Series,  18,  Bur.  Ent.,  U.S. 
Dep't  of  Agric.) 


PHYLUM  ARTHROPODA 


323 


queens  or  workers.  Unfertilized  eggs  are  usually  laid  in  drone 
cells,  and  those  that  develop  become  drones.  How  fertilization 
is  controlled  is  still 
unknown. 

The  egg  undergoes 
superficial  cleavage 
(p.  86,  Fig.  50,  D)  as 
in  the  crayfish  (p.  289). 
A  blastoderm  of  a  single 
layer  of  cells  is  formed 
at  the  surface;  this 
soon  thickens  on  the 
ventral  side,  forming 
a  germ  band.  The 
germ  band  segments, 
sends  out  protrusions 
which  become  append- 
ages, and  grows  until  it 
completely  surrounds 
the  egg.  In  three  days 
the  larva  emerges  from 
the  egg-shell. 

The  changes  that 
take  place  in  an  insect 

1      •        •,                j-i  Fig.   246.  —  Reproductive    organs,    sting,    and 

durmg  Its  growth  con-  p^j^^^    ^^^^^    of    queen    honey-bee.     AGl,    acid 

Stitute      its      metamor-  gland;  AGID,  duct  of  acid  gland;  BGl,  alkaline 

'hhn<:^\         TVip    lifp  Viic  gland;     Ov,    ovary;     ov,    ovarian    tubules;    OvD, 

V"<(i^''^*        ine    nie-ms-  oviduct;    PsnSc,  poison  sac;    Spm,  spermatheca; 

tory   of    an    individual  Stn,    sting;     StnPlp,    sting  feeler;     Vag,   vagina, 

u                      u       J'    -J    J  (From    Snodgrass,    Tech.    Series    18,   Bur.    Ent., 

bee   may    be   divided   u.  S.  Dept.  Agric.) 
into    four    periods 

(Fig.  247):  (i)  egg,  (2)  larva  (FL,  SL),  (7,)  pupa  (N),  (4)  adult 
or  imago  (Fig.  236).  When  the  larva  hatches,  it  lies  at  the 
base  of  the  cell  (Fig.  247,  FL),  floating  in  the  food  prepared  by 
the  workers  and  known  as  chyle  or  "  bee  milk."  Chyle  is  com- 
posed of  digested  honey  and  pollen,  probably  mixed  with  a 


324 


COLLEGE   ZOOLOGY 


glandular  secretion,  and  is  given  to  all  of  the  larvae  by  the 
nurse  bees  during  the  first  three  days.  Then  the  larvae  that  will 
become  workers  are  given  honey  and  digested  pollen  in  gradually 
increasing  amounts;  the  drone  larvae,  after  the  fourth  day,  also 
receive  honey  and  undigested  pollen;  but  the  queen  larvae  are 
fed  lavishly  on  the  rich  albuminous  bee  milk,  the  "  royal  jelly," 
until  they  change  to  pupae. 

Growth  during  the  larval  period  is  accompanied  by  several 
molts  of  the  chitinous  larval  envelope.  At  the  end  of  the  larval 
period  the  cells  containing  the  young  brood  are  covered  over 


Fig.  247.  —  Larvae  and  pupa  of  honey-bee  in  their  cells.  SL,  larva  spin- 
ning cocoon;  N,  pupa;  FL,  young  larva,  an,  antenna;  ce,  eye;  co,  cocoon; 
m,  mandible;  sp,  spiracles;  /,  tongue;  w,  wing.    (From  Packard,  after  Cheshire.) 


with  wax,  feeding  ceases,  and  the  larvae  proceed  to  spin  a  cocoon 
of  silk  from  their  spinning  glands  (Fig.  247,  SL).  These  spin- 
ning glands  become  the  salivary  glands  of  the  adult. 

It  takes  the  worker  thirty-six  hours  to  spin  its  cocoon,  then 
it  slowly  changes  into  a  pupa,  or  chrysalis  (Fig.  247,  N).  Prac- 
tically the  entire  body  is  made  over  at  this  time;  the  three  re- 
gions, head,  thorax,  and  abdomen,  become  distinct;  externally 
the  wings  (w.),  legs,  mouth  parts  (/,  w),  sting,  antennae  {an), 
and  eyes  are  visible;  and  the  internal  changes  are  even  more 
striking,  the  larval  organs  developing  into  those  of  the  adult, 
and  new  organs  appearing.  After  a  period  of  rest  the  pupa  casts 
off  its  exoskeleton,  and  emerges  as  an  adult. 


PHYLUM  ARTHROPODA 


325 


The  Activities  of  the  Workers.  —  All  of  the  duties  necessary 
for  maintaining  a  successful  colony  are  performed  by  the  workers, 
except  mating  with  the  queen,  which  is  accomplished  by  the 
drones,  and  laying  the  eggs,  w^hich  is  done  by  the  queen. 

Building  Honeycomb.  —  The  wax  which  is  used  to  build 
honeycomb  is  secreted  in  thin  scales  by  the  wax  glands.  The 
wax  is  removed  by 
the  wax  pinchers 
(Fig.  238,  B,  wp) 
and  transferred  to 
the  mouth,  where  it  || 
is  mixed  with  saliva   B 


wsm 


Drone  cells 


Transition  cells 
A 


Worker  cells 


and  kneaded  by  the 
mandibles.  If  new 
comb  is  to  be  built, 
the  wax  is  plastered 
to  the  roof,  and  in 
some  mysterious  way 
each  bee  puts  its 
contribution  almost 
exactly  where  it  is 
to  remain.  The  cells 
which  are  built  up 
are  hexagonal  in 
shape  and  of  various 
sizes.  Six  kinds  may 
be  recognized  (Fig. 
248),  (i)  worker  cells 
in  which  workers  are 

reared,  (2)  drone  cells  in  which  drones  develop,  (3)  queen  cells 
which  are  large  and  irregular,  (4)  transition  cells  between  worker 
and  drone  cells,  (5)  attachment  cells  which  fasten  the  comb  to  the 
top  or  sides  of  the  hive,  and  (6)  honey  cells  in  which  honey  is 
stored.  Honey  may  be  stored  also  in  drone,  worker,  and  transi- 
tion cells.     Careful  measurements  have  shown  that  the  cells  are 


Fig.  248.  —  Honeycomb  showing  various  kinds 
of  cells.  A,  diagram  showing  comparative  size  of 
drone  cells  and  worker  cells.  B,  photograph  of  a 
piece  of  honeycomb  showing  circular  cells  and 
attachment  cells.     (From  Root.) 


326  COLLEGE  ZOOLOGY 

seldom  perfectly  symmetrical,  although  in  many  cases  they 
appear  so  to  our  eyes.  The  honey  cells  are  built  with  entrances 
slightly  above  their  bases,  so  that  the  honey  stored  in  them  will 
not  flow  out  before  it  becomes  "  ripe." 

The  Collection  of  Propolis.  —  "  Bee  glue,"  as  propolis  is 
sometimes  called,  is  a  resinous  material  collected  from  buds  and 
crevices  of  trees.  It  is  transported  in  the  pollen  baskets,  and  is 
used,  as  soon  as  collected,  to  paint  the  inside  of  the  hive,  to  fill 
up  cracks,  and  to  strengthen  any  loose  parts. 

Gathering  Pollen.  —  Pollen  grains  are  very  small,  of  various 
shapes  and  colors,  and  are  formed  within  a  part  of  the  flower 
known  as  the  anther.  To  the  bee,  pollen  is  invaluable  as  a  food, 
and  is  also  used  in  preparing  the  cells  containing  pupae.  The 
peculiar  structures  on  the  legs  and  other  parts  of  the  bee's  body 
used  in  collecting  pollen  have  already  been  described  (p.  316). 
Upon  reaching  the  hive  the  pellets  of  pollen  are  pried  out  of  the 
pollen  basket  by  the  spur  at  the  termination  of  the  tibia  of  the 
middle  leg  (Fig.  238,  D,  5),  and  deposited  usually  in  worker 
cells.  Pollen  is  the  principal  food  of  the  larvae.  It  is  very  rich 
in  nitrogenous  material,  a  food  element  not  found  in  honey,  and 
without  which  the  yoimg  would  starve.  The  gathering  of  pollen 
by  bees  has  a  great  influence  upon  the  flowers  visited,  since  many 
species  depend  Upon  bees  for  transporting  pollen  from  one  to 
another. 

Carrying  Water.  —  During  warm  weather  water  is  sucked 
up  into  the  honey  sac  from  dew,  or  brooks  and  pools,  and  carried 
to  the  larvae  in  the  hive. 

The  Manufacture  of  Honey.  —  Bees  do  not  collect  honey 
from  flowers,  but  gather  nectar,  which  is  later  transformed  into 
honey.  The  nectar  is  lapped  up  by  the  tongue  (Fig.  237,  /), 
and  transferred  to  the  honey  sac  (Fig.  241,  hs)^  where  it  is  stored 
while  the  bee  is  in  the  field.  Nectar  is  placed  in  open  cells  in  the 
well- ventilated  hive  until  all  but  18  to  20  per  cent  of  the  water 
contained  in  it  has  evaporated.  When  a  cell  is  finally  filled 
with  "  ripe  "  honey  it  is  sealed  with  a  cap  of  wax.     The  flavor 


PHYLUM   ARTHROPOD  A  327 

of  honey  depends  upon  the  kind  of  flowers  from  which  the 
nectar  is  collected.  The  amount  of  honey  produced  in  one 
hive  in  a  fair  season  ranges  from  an  average  of  about  thirty 
pounds  of  comb  honey  to  possibly  fifty  pounds  of  extracted 
honey.  This  will  net  the  bee  keeper  from  ten  to  fifteen  cents 
per  pound. 

Cleaning  the  Hive.  —  The  health  of  the  swarm  depends 
upon  the  cleanliness  of  their  domicile,  since  perfect  sanitary 
conditions  are  necessary  where  so  many  individuals  live  in  such 
close  quarters.  Dead  bees,  pieces  of  old  comb,  the  excreta  of 
the  queen,  drones,  and  others  that  remain  in  the  hive,  and  any 
other  waste  materials,  are  immediately  removed. 

Ventilating  the  Hive.  —  Fresh  air  for  the  hive  is  obtained 
by  the  exertions  of  certain  of  the  workers.  Many  bees  near  the 
entrance,  and  at  other  places  in  the  hive,  are  busily  engaged  in 
vibrating  their  wings,  and  creating  a  current  of  air,  which  keeps 
the  hive  fresh,  and  aids  in  ripening  the  nectar.  The  loud  buzzing 
which  accompanies  this  activity  is  often  heard  at  night  after  a 
large  amount  of  nectar  has  been  collected. 

Guarding  the  Hive.  —  The  hive  is  guarded  against  the  in- 
trusions of  yellow-jackets,  bee-moths,  and  other  bees  by  workers, 
who  wander  back  and  forth  near  the  entrance,  and  examine 
every  creature  that  visits  the  colony.  If  the  swarm  is  strong, 
the  guards  succeed,  with  the  aid  of  the  bee-keeper,  in  warding 
off  all  honey-loving  enejnies. 

Swarming.  —  The  number  of  bees  in  a  hive  increases  very 
rapidly,  since  the  queen  usually  lays  from  950  to  1200  eggs  per 
day.  When  the  colony  is  in  a  prosperous  condition,  and  there 
is  danger  of  overcrowding,  queen  cells  are  built  by  the  workers, 
usually  around  the  fertiUzed  eggs,  and  new  queens  are  reared. 
Two  queens  do  not  live  amicably  in  one  hive,  and,  if  such  a  con- 
dition arises,  either  there  is  a  battle  between  the  two,  resulting 
in  the  death  of  one  of  them,  or  the  workers  kill  one,  or  else  the 
old  queen  collects  from  two  to  twenty  thousand  workers  about 
her  and  flies  away  with  them  to  found  a  new  colony.     This  is 


328  COLLEGE  ZOOLOGY 

known  as  swarming.  The  old  hive  is  not  broken  up,  but  continues 
its  existence  as  before. 

Swarming  occurs  in  May,  June,  or  July,  according  to  latitude, 
and  a  second  swarming  period  may  be  inaugurated  if  weather 
conditions  result  in  a  midsimimer  flow  of  honey.  Before  issuing 
from  the  hive,  the  honey  sacs  are  filled  with  honey  to  serve  until 
a  new  home  is  found.  The  swarm,  after  flying  a  short  distance, 
comes  to  rest  upon  the  limb  of  a  tree  or  other  object,  where  it 
remains  sometimes  for  several  hours.  A  site  for  the  new  colony 
is  sometimes  chosen  by  scouting  bees  several  days  before  the 
swarm  leaves  the  parent  hive.  These  scouts  may  also  partially 
prepare  the  place  by  cleaning  out  loose  dirt,  bark,  etc.  The 
usual  choice  is  a  hollow  tree,  such  as  the  wild  ancestors  of  the 
honey-bee  inhabited,  and  henceforth  is  called  a  "  bee  tree.' ■  One 
of  the  duties  of  the  bee-keeper  is  to  hive  the  swarms  before  they 
succeed  in  escaping  to  the  woods.  Swarms  may  also  be  formed 
artificially. 

The  Enemies  and  Diseases  of  Bees.  —  The  bee-moth, 
Galleria  mellionella,  bee-louse,  Braula  cceca,  kingbird,  toad, 
lizard,  spider,  rat,  skunk,  bear,  and  other  bees  are  all  enemies  of 
the  honey-bee.  Weak  or  neglected  hives  are  especially  liable  to 
attack,  and  the  bee-keeper  is  often  obliged  to  help  his  bees  com- 
bat the  foe.  The  principal  diseases  of  bees  are  foul  brood,  which 
is  an  infectious  disease  due  to  bacteria,  and  dysentery,  which  is 
usually  caused  by  improper  food  or  long  confinement  in  the 
hive. 

b.  The  Anatomy  and  Physiology  of  Insects  in  General 

There  are  a  larger  number  of  species  of  insects  known  than  of  all 
other  animals  combined.  Over  three  hundred  thousand  have 
been  described  and  the  number  still  unknown  can  only  be 
imagined.  The  number  of  individuals  of  many  species  is  also 
enormous.  Insects  range  in  size  from  jW  mm.  long  (certain 
parasites)  to  over  155  mm.  in  length  {Dynastes  hercules,  the 
Venezuelan  beetle). 


PHYLUM   ARTHROPODA 


329 


Anatomy      and 
Physiology.— The 
honey-bee     is    a 
highly  specialized 
insect     and     ex- 
hibits  adaptive 
structures  to  a  re- 
markable  extent. 
It  does  not,  how- 
ever, illustrate 
general     anatom- 
ical    features    as 
well  as  some  other 
species,    e.g.    the 
grasshopper  (Fig. 
249).    An  insect's 
body   consists   of 
three    principal 
parts,    (i)    head, 
(2)  thorax,  (3)  ab- 
domen.   The  head 
bears  a  compound 
eye  on  either  side, 
three  simple  eyes 
(ocelli)  and  a  pair 
of     antennae     in 
front,    a    frontal 
piece    called    the 
clypeus,  and  four 
pairs  of   append- 
ages  constituting 
the  mouth-parts. 
The  thorax  con- 
tains   three    seg- 
ments, —  protho- 


330 


COLLEGE  ZOOLOGY 


rax,  mesothorax,  and  metathorax.  The  mesothorax  and  meta- 
thorax  bear  each  a  pair  of  wings  in  most  insects.  Certain 
simple  species  (Aptera,  p.  337,  Fig.  259)  do  not  possess  wings; 
others  (lice  and  fleas,  pp.  341  and  359,  Figs.  266  and  296)  have 

no  wings,  but  this  is  because  they 
are  degenerate.  The  flies  (Diptera, 
p.  356,  Fig.  292)  have  a  pair  of 
clubbed  threads,  called  balancers 
or  halters,  in  place  of  the  meta- 
thoracic  wings.  Attached  to  each 
thoracic  segment  is  a  pair  of  legs. 
The  parts  of  a  thoracic  se^vjgit 
are  well  shown  in  the  grasshopper. 
The  dorsal  part,  the  tergum,  is 
composed  of  four  pieces,  termed 
sclerites,  which  are  especially 
marked  on  the  prothoracic  seg- 
ment. They  are  named  the  prcE- 
scutum,  scutum,  scutellum,  and  post- 
scutellum.  The  side  of  a  thoracic 
Fig.  250.  —  Different  forms  of    segment  is  called  the  pleurum;  it 

antennae  of  insects,     a,  bristle-like  .  .       .  7     . , 

consists    of    three    sclerites,    the 


episternum,  epimeron,  and  parap- 
teron.  The  underside  of  each 
thoracic    segment    is    called    the 


a,  bristle-like 
antenna  of  a  grasshopper,  Locusta; 

b,  filiform,  of  a  beetle,    Carabus  ; 

c,  moniliform,  of  a  beetle,  Tenebrio; 

d,  dentate,    of    a    beetle,    Elater ; 

e,  pectinate,  of  Ctenicera;  f,  crooked, 
of  honey-bee.  Apis ;  g,  club-shaped, 
of  beetle,  Silpha:   h,  knobbed,  of     sternum. 

beetle,  Necrophorus; y^mell^ted        The   abdomen    is    made    up    of 

of    beetle,    Mclolontha;     k,    with        i— — ^— — — — 

bristle,  from  fly,  Sargus.  (From  eleven  segments.  The  posterior 
Sedgwick's  Zoology,  after  Bur-  ^^d  in  the  female  is  usually  modi- 
meister.)  r    ^   ^  1      •  /      . 

fied  by  egg-laying  structures  {ovi- 
positors), and  in  the  male  by  a  copulatory  apparatus  {genitalia). 
The  abdomen  is  usually  punctured  by  seven  pairs  of  breathing 
pores  (spiracles)  and  the  thorax  generally  by  two  pairs. 

The  antennae,  mouth-parts,  legs,   and  wings  are  among  the 
most  interesting  external  features  of  insects.     The  antenna  are 


PHYLUM   ARTHROPODA 


33^ 


usually  tactile,  olfactory,  or  auditory  in  function.  They  differ 
widely  in  form  and  structure,  as  shown  in  Figure  250.  Often 
the  antennae  of  the  male  differ  from  those  of  the  female. 

The  mouth-parts  of  insects  are  in  most  cases  fitted  either  for 
biting  (mandibulate)  or  sucking  (suctorial).  The  cockroach  pos- 
sesses typical  mandibulate  moutlj- 
parts  (Fig.  251)  consisting  of  an 
upper  lip,  the  labrum,  a  lower  lip, 
the  labium  (B),  a,  pair  of  jaw^s,  the 
mandibles  (C),  and  a  pair  of  auxil- 

L.in 


Fig.  251.  —  Mouth  parts  of  a  cockroach, 
Periplaneta.  A,  ist  maxilla.  C,  cardo ; 
L.ex,  galea;  L.in,  lacinia;  Mxt,  maxillary 
palpus;  St,  stipes.  B,  labium  or  lower  lip; 
lettering  as  above.  C,  mandible  {Md). 
(From  Sedgwick's  Zoology,  after  Savigny.) 


Fig.  252.  —  Mouth  parts 
of  a  mosquito,  Culex  memo- 
rosus.  H,  hypopharynx  for 
piercing;  Lb,  lower  lip  or 
proboscis;  Lbr,  upper  lip; 
Lt,  labial  palp;  Md,  mandi- 
bles; Mx,  maxillae.  (From 
Sedgwick's  Zoology,  after 
Becher.) 


iary  jaws,  the  maxillce  {A).  The  labium  and  maxillae  bear 
jointed  feelers  or  palps  {Mxt)  which  function  as  sense-organs. 
The  labrum  and  labium  hold  the  food  while  it  is  being  mas- 
ticated by  the  mandibles  and  maxillae.  The  mandibles  of  insects 
that  live  on  vegetation  are  adapted  for  crushing;  those  of 
carnivorous  species  are  usually  sharp  and  pointed,  being  fitted 
for  biting  and  piercing.     Suctorial  mouth-parts  are  adapted  for 


332 


COLLEGE   ZOOLOGY 


piercing  the  tissues  of  plants  or  animals  and  sucking  juices. 
The  mouth-parts  of  the  honey-bee  (Fig.  237)  are  suctorial,  but 
highly  modified.  In  the  female  mosquito  (Fig.  252)  the  labrum 
and  epipharynx  combined  {Lhr)  form  a  sucking  tube;  the 
mandibles  {Md)  and  maxillae  {Mx)  are  piercing  organs;  the 
hypopharynx  {H)  carries  saliva;  and  the  labium  {Lh)  con- 
stitutes a  sheath  in  which  the  other  mouth-parts  lie  when  not 


Fig.  253.  —  Mouth  parts 
of  a  moth,  Noctua.  A,  an- 
tenna ;  Lr,  upper  lip ; 
Lt,  where  labial  palp  has 
been  cut  away;  Mx,  maxilla; 
Mxt,  maxillary  palp:  Oc,  eye. 
(From  Sedgwick's  Zoology, 
after  Savigny.) 


Fig.  254.  —  Different  forms  of  legs  of  insects. 

a,  predatory    leg    of  praying-mantis,    Mantis; 

b,  running  leg  of  a  beetle,  Carabus ;  c,  leaping 
leg  of  a  grasshopper,  Acridium  ;  d,  digging  leg 
of  mole-cricket,  Gryllotalpa ;  e,  swimming  leg  of 
Dytiscus.  (From  Sedgwick's  Zoology,  after 
regne  animal.) 


in  use  (Dimmock).  The  proboscis  of  the  butterflies  and  moths 
(Fig.  253,  Mx)  is  a  sucking  tube  formed  by  the  maxillae. 

The  mouth -parts  of  insects  are  of  considerable  importance 
from  an  economic  standpoint,  since  insects  that  eat  solid  food 
can  be  destroyed  by  spraying  the  food  with  poisonous  mixtures, 
whereas  those  that  suck  juices  must  be  smothered  with  gases  or 
have  their  spiracles  closed  with  emulsion. 

The  le^s  of  insects  are  used  for  various  purposes  and  are  highly 


PHYLUM   ARTHROPODA 


333 


modified  for  special  functions.  Those  of  the  honey-bee  have 
already  been  described  (pp.  314  and  316,  Fig.  238).  A  typical 
leg  consists  of  five  parts,  —  coxa  (Fig.  238,  B,  c),  trochanter  (/r), 
femur  (/),  tibia  {ti),  and  tarsus  (/).  The  tarsus  (Fig.  239)  is 
usually  composed  of  five  segments  and  bears  at  the  end  a  pair 
of  claws  (an)  J  between  which  is  a  fleshy  lobule,  the  pulvillus  (pv), 
Figure  254  shows  a  number^ of  legs  adapted  for  different  uses. 
Running  insects  possess  long,  slender  legs  (b);  the  mantis  (a) 
has  its  fore  legs  fitted  for  grasping;  the  hind  legs  of  the  grass- 
hopper (c)  are  used  in  leaping;  the  fore  legs  of  the  mole  cricket 


v^ 


Fig.  255. — The  right  wing  of  a  male  mosquito,  Anopheles  maculipennis. 
A,  anal  area;  ist  A,  anal  nervure;  C,  costa;  Cu,  cubitus;  H,  humeral  cross- 
nervure;  /,  cross-nervure  between  Ri  and  /?4+5;  /,  cross-nervure  between 
radial  and  medial  systems;  K,  cross-nervure  between  medial  and  cubital  sys- 
tems; M,  media;  0,  cross-nervure  between  Ri  and  Rr,  R,  radius;  Sc,  sub- 
costa.     (From  Sedgwick's  Zoology,  after  Nuttall  and  Shipley.) 

{d)  are  modified  for  digging;  and  the  hind  legs  of  the  water 
beetle  {e)  are  fitted  for  swimming.  Many  other  types  could  be 
mentioned. 

The  win^s  of  insects  enable  their  owners  to  fly  rapidly  from 
place  to  place  and  thus  to  escape  from  enemies  and  to  find  a 
bountiful  food  supply.  The  success  of  insects  in  the  struggle  for 
existence  is  in  part  attributed  to  the  presence  of  wings.  Wings 
are  outgrowths  of  the  skin  strengthened  by  a  framework  of 
chitinous  tubes,  called  veins  or  nervures,  which  divide  the  wing 
into  cells.  The  veins  varv  in  distribution  in  different  species, 
but  are  quite  constant  in  individuals  of  any  given  species;  they 
are  consequently  used  to  a  considerable  extent  for  luirposes  of 
classification.  The  principal  longitudinal  veins,  as  shown  in 
Figure  255,  are  the  cosla  (C),  subcosta  {Sc),  radius  (R),  media 


334 


COLLEGE  ZOOLOGY 


(M),  cubitus  (Cu),  and  anal  (A).  Cross  veins  (/,  /,  K) 
frequently  occur.  Modifications  come  about  by  reduction 
or  by  addition.  In  the  beetles  (Coleoptera)  the  fore-wings 
are  sheath-like,  and  are  called  elytra.  The  fore-wings  of 
Orthoptera  (grasshoppers,  etc.)  are  leathery  and  are  known 
as  tegmina. 

Of  the  internal  organs  of  insects  the  alimentary  canal  and  res- 
piratory systems  are  of  particular  interest.  The  alimentary 
canal  is  modified  according  to  the  character  of  the  food.  An 
insect  with  mandibulate  mouth-parts  (Fig.  256)  usually  pos- 
sesses (i)  an  (Esophagus  iOe)  which  is  dilated  to  form  a  crop  (Jn) 
in  which  food  is  stored,  (2)  a  muscular  gizzard  or  proventriculus 
(Pv)  which  strains  the  food  and  may  aid  in  crushing  it,  (3)  a 
stomach  or  ventriculus  (Chd)  into  which  a  number  of  glandular 
tubes  {gastric  cceca)  pour  digestive  fluids,  and  (4)  an  intestine  (R) 
with  urinary  or  malpighian  tubules  (Mg)  at  the  anterior  end. 
Suctorial  insects,  like  the  butterflies  and  moths  (Fig.  257),  are 
provided  with  a  muscular  pharynx  which  acts  as  a  pumping  organ 
and  a  sac  (  V)  for  the  storage  of  juices. 

The  respiratory  system  of  insects  is  in  general  like  that  of  the 
honey-bee  (p.  320,  Figs.  242  and  243),  but  modifications  occur  in 
many  species,  especially  in  the  larvae  of  those  that  live  in  water. 
Aquatic  larvae,  in  many  cases,  do  not  have  spiracles,  but  get 
oxygen  by  means  of  thread-like  or  leaf-like  cuticular  outgrowths 
at  the  sides  or  posterior  end  of  the  body,  termed  tracheal  gills 
(Fig.  261,  A).  Damsel-fly  larvae  possess  caudal  tracheal  gills, 
and  the  larvae  of  the  dragon- flies  take  water  into  the  rectum 
which  is  lined  with  papillae  abundantly  supplied  with  tracheae. 
The  economic  importance  of  a  tracheal  respiratory  system  has 
already  been  pointed  out  (p.  332). 

Growth  and  Metamorphosis.  —  Three  types  of  insects  may 
be  distinguished  with  respect  to  the  method  of  their  develop- 
ment, (i)  ametabola,  (2)  heterometabola,  and  (3)  holometabola. 
The  ametabolous  insects  are  essentially  like  the  "adult,  except  in 
size,  when  they  hatch  from  the  egg;   they  develop  to  maturity 


PHYLUM  ARTHROPODA 


335 


without  a  metamorphosis.    The  Aptera  (p.  337,  Fig.  259)  are 
ametabolous. 

The  heterometabolous  insects  hatch  from  the  egg  and  develop 
into  adults  without  passing  through  a  true  pupal  period.  In  the 
grasshopper,  for  example  (Fig.  258),  the  young  resembles  the 


Fig.  256.  —  Alimentary 
canal  and  glandular  ap- 
pendages of  a  beetle,  Cara- 
bus.  Ad,  anal  glands  with 
vesicle;  Chd,  chylific  ven- 
tricle; Jn,  crop;  Mg,  mal- 
pighian  tubule;  Oe,  oesoph- 
agus; Pv,  proventriculus ; 
R,  rectum.  (From  Sedg- 
wick's Zoology,  after  Du- 
four.) 


Fig.  257.  —  Longitudinal  sec- 
tion through  the  body  of  a  moth, 
Sphinx  ligustri,  showing  the  ali- 
mentary canal  of  a  sucking  insect. 
A,  anus;  At,  antenna;  E,  rectum; 
G,  testis;  Gi,  subcesophageal 
ganglion;  Gs,  brain;  H,  heart; 
M,  mesenteron ;  Mx,  maxillae 
forming  proboscis ;  N,  thoracic 
and  abdominal  ganglia;  /,  palp; 
V,  oesophagus ;  V^,  suctorial 
stomach;  Vm,  malpighian  tubules. 
(From  Sedgwick's  Zoology,  after 
Newport.) 


336 


COLLEGE  ZOOLOGY 


adult  except  for  the  absence  of  wings  and  mature  reproductive 
organs.  Such  a  stage  is  usually  spoken  of  as  a  nyMph.  Orders 
II  to  XI  of  Table  XII  contain  heterometabolous  insects.  Many 
of  the  species  belonging  to  these  orders  change  considerably 
during  their  growth  period,  but  they  are  all  more  or  less  active 


Fig.  258.  —  Partial  metamorphosis  of  a  grasshopper,  Melanoplus  femur- 
rubrum,  showing  the  five  nymph  stages,  and  the  gradual  growth  of  the  wings. 
(From  Packard,  after  Emerton.) 

throughout  their  development  and  are  said  to  undergo  direct 
or  incomplete  metamorphosis. 

Holometabolous  insects,  such  as  the  honey-bee  (Fig.  247),  pass 
through  both  a  larval  and  a  pupal  stage  in  their  development. 
The  majority  of  insects Jbelgng  to  this  type  (Table  XII,  orders 
XII  to  XIX). 


c.  General  Survey  of  the  Orders  of  Insects 

Classification.  —  Insect  classification  is  based  principally  on 
the  following  characteristics:  (i)  the  presence  or  absence  of 
wings,  and  their  structure  when  present,  (2)  the  structure  of  the 
mouth-parts,  and  (3)  the  character  of  the  metamorphosis.  Au- 
thorities differ  with  regard  to  the  number  of  orders  that  should 
be  recognized,  and  two  rather  definite  classifications  have  re- 


PHYLUM  ARTHROPODA 


337 


suited;  these  are  known  as  (i)  the  condensed  classification,  and 
(2)  the  extended  classification,  and  are  correlated  in  Table  XII. 
Because  of  the  large  number  of  orders  space  will  permit  only  a 
few  words  about  each.  Illustrations  have  been  provided  to 
show  the  principal  characteristics. 


TABLE   XII 
> 

;:!oND 

ENSED  Classification  Extended  Ci.assifi 

Order 

Order 

I. 

Aptera       .... 

.      I 

Aptera  . 

'       II 

Ephemerida    . 

III 

Odonata     .     . 

IV 

Plecoptera 

n. 

Pseudoneuroptera   ■ 

V 

Isoptera     .     . 

VI 

Corrodentia    . 

VII 

Mallophaga    . 

VIII 

Thysanoptera 

in 

Orthoptera  .     .     A 

IX 
X 

Euplexoptera 
Orthoptera 

IV 

Hemiptera   .     .     . 

.    XI 

Hemiptera      . 

XII 

Neuroptera    . 

V. 

Neuroptera  .     .     . 

XIII 

Iklecoptera 

.  XIV 

Trichoptera    . 

VI. 

Lepidoptera .     .     ._ 

.  XV 

Lepidoptera    . 

'   XVI 

Diptera      .     . 

VII. 

Diptera    .     .     .     .^ 

.XVII 

Siphonaptera 

\iiii. 

Coleoptera    ... 

XVIII 

Coleoptera 

IX 

Hymenoptera    .     . 

XIX 

Hymenoptera 

Common  Names 

Springtails,  fish-moths. 

May-flies. 

Dragon-flies. 

Stone-flies. 

Termites  or  white  ants. 

Book-lice,  bark-lice. 

Biting  bird-Uce. 

Thrips. 

Earwigs. 

Grasshoppers,  crickets, 
cockroaches. 

Lice,  bugs,  plant-lice. 

Ant-lions,  hellgramite 
flies. 

Scorpion  flies. 

Caddice-flies. 

Moths,  skippers,  but- 
terflies. 

Flies,  sheep-ticks. 

Fleas. 

Beetles. 

Ants,  wasps,  bees,  saw- 
flies,  ichneumon-flies. 

Order  i.  Aptera.  —  Springtmls  and  Fishmoths  (Figs. 
259,  260).  —  Insects  without  wings,  probably  descended  from 
wingless  ancestors;  biting  mouth-parts  retracted  within  the 
cavity  of  the  head;   no  metamorphosis. 

The  very  primitive  living  insect,  Campodea  staphylimis  (Fig. 
259),  belongs  to  this  order.  The  most  common  species  is  the 
fishmoth,  Lepisma  saccharina  (Fig.  260),  which  lives  on  dry 
starchy  food  such  as  book  bindings  and  starched  clothing.     An- 


33^ 


COLLEGE  ZOOLOGY 


Fig.  259.  —  Order 
Aptera.  Campodea 
staphylinus.  (From 
Sedgwick's  Zoology, 
after  Lubbock.) 


Fig.  260.  —  Order 
Aptera.  Lepisma 
saccharina,  the  fish- 
moth.  (From  Sedg- 
wick's Zoology.) 


other  interesting  species 
is  the  snow-flea,  Achorutes 
nivicola,  which  is  some- 
times a  pest  in  maple 
sugar  camps,  since  large 
numbers  collect  in  the 
sap. 

Order  2.    Ephemerida. 

—  May-flies  (Fig.  261). 

—  Insects  possessing  deli- 
cate membranous  wings, 
with  many  cross  veins ; 
the  fore-wings  large,  the 
hind  wings  small  or  want- 
ing; mouth-parts  poorly 
developed;  metamorpho- 
sis incomplete. 

The  young  (nymph)  may- fly  (Fig.  261,  A)  lives  in  the  water 
and  breathes  by  means 
of  tracheal  gills.  After 
from  one  to  three 
years,  depending  upon 
the  species,  the  nymph 
emerges  from  the 
water  and  becomes  a 
winged  adult  (Fig. 
261,  B).  This  adult 
is  said  to  be  in  the 
subimago  stage,  since 
it  moults  after  acquir- 
ing wings.  No  other 
insect  is  known  to  do 
this.     The  paired  con- 


FiG.  261. — Order  Ephemerida 
gills;    /,  principal  trunk  of  tracheal  system 
filaments.     (From  Sedgwick's  Zoology.) 


A      *  B 

A,   nymph  of  the  May- fly 


k,   tracheal 
B,   adult  May- fly.      Af,    anal 


PHYLUM  ARTHROPODA  339 

dition  of  the  egg  ducts  of  the  female  is  also  unique.  Adult  may- 
flies probably  take  no  food;  they  mate,  lay  their  eggs,  and,  after 
a  few  hours,  die. 

Order  3.  Odonata.  —  Dragon-flies  and  Damsel-flies 
(Fig.  262).  —  Insects  possessing  four  membranous  wings,  with 
many  cross  veins;  hind  wings  as  large  as  or  larger  than  fore- 
wings;  each  wing  with  joint,  thd*  nodus,  on  front  margin;  biting 
mouth-parts;  metamorphosis  incomplete. 

The  dragon- flies  are  also  called  darning-needles  and  snake 
doctors.  When  at  rest  they  hold  their  wings  horizontally,  differ- 
ing in  this  respect  from  the  damsel- flies,  which  hold  their  wings 


Fig.  262.  —  Order  Odonata.     A  dragon-^y,  Libellula  depressa. 
(From  Miall,  alter  Charpentier.) 

vertically  over  their  backs.  The  adult  dragon- flies  devour  large 
numbers  of  mosquitoes,  but  unfortunately  feed  only  by  day, 
whereas  some  of  the  mosquitoes  are  most  active  after  dark. 
The  young  live  in  the  water;  they  breathe  by  drawing  in  and 
expelling  water  from  the  rectum,  which  is  lined  with  tracheal 
gills.  The  damsel- flies  are  more  delicate  than  the  dragon- flies. 
Their  young  possess  leaf-like  tracheal  gills  at  the  posterior  end 
of  the  body.  The  compound  eyes  of  the  Odonata  are  made 
up  of  an  enormous  number  of  elements  (ommatidia) ;  more  thaa 
30,000  facets  have  been  counted  in  the  eye  of  one  species. 


340 


COLLEGE  ZOOLOGY 


Order  4.  Plecoptera.  —  Stone-flies 
(Fig.  263).  — Insects  with  four  membranous 
wings;  hind  wings  large  and  folded  like  a 
fan;  biting  mouth-parts;  metamorphosis 
incomplete. 

The  stone- fly  nymphs  live  in  brooks  on 
the  underside  of  stones,  and  breathe  by 
means  of  filamentous  tracheal  gills  which 
extend  out  from  just  behind  the  legs.  They 
serve  as  food  for  fishes. 

Order  5.  Isoptera.  — Termites  or  White 
Ants  (Fig.  264).  —  Insects  with  four  similar 
wings,  leathery  in  structure  and  lying  flat 
on  the  back,  or  wingless  (workers);  biting 
mouth-parts;  metamorphosis  incomplete.  -  j 

The  termites  are  social  insects  and  live 
in  colonies.  Each  colony  contains  a  queen 
(Fig.  264,  B)  that  lays  all  of  the  eggs,  a 
winged  male  (A)  that  fertilizes  the  queen,  a 
number  of  wingless  workers  (C)  that  build  the  nest,  procure 


Fig.  263.  —  Order 
Plecoptera.  Stone- 
fly,  Perla  maxima. 
(From  Sedgwick's 
Zoology,  after  Pictet.) 


D 

Fig.  264.  —  Order  Isoptera.  Termites. 
A,  male  or  king  of  Termes.  B,  female  or 
queen  of  Termes.  C,  worker  of  Termes. 
D,  soldier  of  Termes.  (From  the  Cambridge 
Natural  History;    C  and  D,  after  Grassi.) 


PHYLUM   ARTHROPODA 


341 


Fig.    265.  —  Order    Corrodentia.     A 
bark-louse,  Psoctts.     (From  Brehm.) 


food,  and  raise  the  young,  and  wingless  soldiers  (D)  whose  duty 
it  is  to  protect  the  colony.  The  food  of  termites  consists  prin- 
cipally of  dead  wood,  and  in  the  tropics  of  Africa  and  South 
America,  where  white  ants  abound,  a  good  deal  of  damage  is 
done  to  houses,  furniture,  etc.  Even  in  North  America  injuries 
to  the  timbers  in  buildings  and 
to  books  in  libraries  have  been 
reported.  The  termites  work 
only  in  the  dark,  and  build 
tunnels  for  this  purpose.  Their 
nests  are  often  inhabited  by 
other  species  of  insects;  these 
are  called  termitophiles.  Over 
one  hundred  species  of  termi- 
tophiles have  been  recorded. 

Order   6.      Corrodentia. 
Book-lice     and     Bark-lice 

(Fig.  265).  —  Insects  without  wings  or  with  four  membranous 
wings,  with  few  cross  veins;  fore-wings  larger  than  hind  wings; 
wings  held  roof-like  over  body;  biting  mouth- 
parts;  metamorphosis  incomplete. 

Book-lice  are  wingless  insects  often  found 
in  old  books,  the  paper  and  bindings  of  which 
they  devour.  Bark-lice  (Fig.  265)  have 
wings.  They  live  out  of  doors  on  tree 
trunks  and  feed  on  lichens. 

Order  7.  Mallophaga.  —  Biting  Bird- 
lice  (Fig.  266).  —  Parasitic  insects  without 
wings;  biting  mouth-parts;  metamorphosis 
incomplete. 

Bird-Hce  live  among  the  feathers  of  birds 
or  hair  of  mammals.  They  eat  hair,  feathers, 
and  epidermal  scales,  but  are  not  injurious 
on  this  account.  The  irritation  caused  by 
their  sharp  claws  makes  their  hosts  restless 


Fig.  266.  —  Order 
Mallophaga.  Biting 
bird-louse,  Menopon 
pallidum,  inhabiting 
the  common  fowl. 
(From  Sedgwick's 
Zoology,  after  Piaget.) 


342 


COLLEGE  ZOOLOGY 


and  consequently  weak 
and  thin.  Chickens  take 
dust  baths  to  rid  them- 
selves of  Menopon  pal- 
lidum (Fig.  266),  the  most 
common  species. 

Order  8.  Thysanop- 
ter.a. — Thrips  (Fig.  267). 
—  Insects  with  four 
narrow,  membranous 
wings  fringed  with  long 
hairs;  mouth-parts  inter- 
mediate ;  the  metamor- 
phosis   transitional,    not 

Fig.   267.  —  Order  Thysanoptera.     Pear  ,  , 

thrips,  Euthrips  pyri.     (From  Moulton,  Bui.    Complete,  but  a  qUieSCent 
80,  Bur.  Ent.,  U.  S.  Dept.  Agric.)  Stage  OCCUrS. 

The  feet  of  these  insects  are  without  claws,  their  place  being 
taken  by  bladders  adapted  for  clinging  to 
leaves  or  flowers.  The  males  are  not  com- 
mon, since  parthenogenesis  is  the  usual 
method  of  reproduction.  Several  species 
are  distinct  pests;  these  are  the  onion- thrips 
{Thrips  tabaci),  the  wheat- thrips  {Euthrips 
tritici),  the  grass- thrips  {Anaphothrips  stri- 
atus),  and  the  fruit  thrips  {Euthrips  pyri) 
(Fig.  267). 

Order  9.  Euplexoptera.  —  Earwigs  (Fig. 
268). — Insects  usually  with  four  wings; 
fore-wings  leathery,  small,  and  veinless; 
biting  mouth-parts;  posterior  end  of  ab- 
domen bears  pair  of  forceps;  metamorphosis 
incomplete.  ^  ^  ^^^    268.  -  Order 

This    order    contains    the    family    FoRFI-    Euplexoptera.     Ear- 

CULID^.     The  earwigs  are  not  common  in  Zi^'^'^D^t 
North  America.     They  feed  at  night  on  fruit   port.) 


PHYLUM  ARTHROPODA 


343 


and  flowers,  but  are  not  of  any  economic  importance  in  this 
country. 

Order  lo.  Orthoptera. — Cockroaches,  Walking-sticks, 
Mantids,  Grasshoppers,  Locusts,  Katydids,  and  Crickets 
(Figs.  269-274).  —  Insects  with  four 
wings ;  the  fore- wings  leathery;  the 
hind  wings  folded  like  a  fan;  biting 
mouth-parts ;  metamorphosis  incom- 
plete. 

The  principal  families  of  Orthop- 
tera are  as  follows : 

(i)  Blattid^e  (Cockroaches,  Fig. 
269).  These  insects  have  legs  fitted 
for  running.  The  common  American 
species  are  the  "  croton-bug  "  {Ectobia 
germanica)  which  was  introduced  from 
Germany,  and  the  "black-beetle" 
(Periplaneta  orientalis,  Fig.  269)  from 
Asia. 

(2)  Mantids    (Praying-Mantis, 

Fig.  270).     The  fore  legs  of  these  insects  are  fitted  for  grasping. 
Their  food  consists  largely  of  other  insects. 

(3)  Phasmid^  (Walking-sticks,  Fig.  271).  The  legs  of 
the  phasmides  are  adapted  for  walking.  Walking-sticks  feed 
on  foliage  and  are  difficult  to  distinguish  from  twigs,  hence  their 
name. 


Fig.  269. — Order  Orthop- 
tera. Cockroach,  Periplaneta 
orientalis.  (From  Sedgwick's 
Zoology.) 


270.  —  Order  Orthoptera.     Praying-mantis,  Phasmomantis  Carolina. 
(From  Davenport,  after  Packard.) 


344 


COLLEGE  ZOOLOGY 


Fig.  272.— -Order   Orthoptera.     Rocky  Moun- 
tain   grasshopper    or    locust,    Melanoplus    spretus. 

a,  a,  a,  females  in  different  positions,  laying  eggs; 

b,  egg-pod  taken  from  ground,  with  end  broken 
open;  c,  eggs  lying  loose  on  ground;  d,  e,  earth 
partly  removed  to  show  egg  mass  in  place  (e)  and 
one  being  placed  {d);  f,  where  egg  mass  has  been 
covered  up.  (After  Riley,  from  Yearbook  Dept 
Agric,  1908.) 


Fig.  271.— Order  Or- 
thoptera. The  north- 
ern "  walking-stick," 
Diapheromera  femorata. 
(From  Davenport.) 


Fig.  274.  — Order 
Orthoptera. 
House-cricket,  Gryl- 
lus  domesticus. 
(From  the  Cam- 
bridge Natural  His- 
tory.) 


273.  —  Order  Orthoptera.     Katydid,  Microcentrum  retinerve. 
(From  Sedgwick's  Zoology,  after  Riley.) 


PHYLUM   ARTHROPODA 


345 


(4)  AcRiDiiD^  (Locusts  or  Short-horned  Grasshoppers, 
Fig.  272).  The  locusts  have  leaping  legs  and  short  antennae. 
They  feed  on  vegetation  and  often  do  considerable  damage. 
The  most  famous  species  is  Melanoplus  spretus,  the  Rocky 
Mountain  locust  (Fig.  272),  which  is  occasionally  migratory 
and  devours  everything  in  its  path.  The  red-legged  locust, 
Melanoplus  femur-rubrum,  and  th«  Carolina  locust,  Dissosteira 
Carolina,  are  common  species. 

(5)  LocusTiD^  (Long-horned  Grasshoppers,  Fig.  273). 
The  members  of  this  family  have  slender  antennae  longer  than 
the  body.     The  meadow  grasshoppers  and  katydids  belong  here. 

(6)  GRYLLID.E  (Crickets,  Fig.  274).  The  mole  crickets 
burrow  in  the  ground;  the  true  crickets  are  those  that  make 
themselves  known  by  their  chirping  about  houses;  the  tree 
crickets  inhabit  trees. 

Order  II.  Hemiptera. — Bugs,  Lice,  Aphids,  Scale  Insects 
(Fig.  275-279).  —  Insects  without  wings  or  with  four  wings; 
one  suborder  with  fore-wings  thickened 
at  base;  sucking  mouth-parts;  meta- 
morphosis incomplete. 

Hemiptera  may  be  separated  con- 
veniently into  three  suborders. 

(i)  Parasitica  (Lice,  Fig.  275). 
This  suborder  is  represented  in  North 
America  by  a  single  family,  the  Pedi- 
CULID^.  These  are  wingless  and  para- 
sitic on  the  bodies  of  man  and  other 
mammals.  They  have  claws  fitted  for 
clinging  to  hairs,  and  an  unjointed 
beak  for  penetrating  the  skin  and  suck- 
ing juices.     The  species  infesting  man 

are    Pediculus    capitis,     the    head-louse    bridge  Natural  History,  after 

Piaget.) 

(Fig.  275),  p.  vestimenti,  the  body-louse, 

and  Phthirius  inguinalis,  the  crab-louse.     Domestic  animals  are 

infested  by  members  of  the  genus  Hcematopinus.     H.  piliferus 


Fig.  275.  —  Order  Hemip- 
tera. Head-louse,  Pediculus 
capitis.       (From    the     Cam- 


346 


COLLEGE  ZOOLOGY 


Fig.  276.  —  Order  Hemiptera. 
Grape-louse,  Phylloxera  vastatrix. 
a,  wingless  form,  b,  same,  ventral 
surface,  c,  winged  form.  (From 
Sedgwick's  Zoology.) 


is  the  dog-louse,  H.  urius,  the 
hog-louse,  and  H.  spinulosuSj 
the  rat-louse. 

(2)  HoMOPTERA  (Plant-lice, 
Scale  Insects,  Cicadas,  Tree 
Hoppers,  Spittle  Insects,  Figs. 
276-278).  The  Homopter A  have 
wings,  when  present,  similar  in 
thickness,  and  a  jointed  beak 
which  arises  from  the  posterior, 
ventral  part  of  the  head. 

The  plant-lice  or  aphids  (Family 
Aphidiid^,  Fig.  276)  are  of  con- 
siderable biological  and  economic 
importance.  They  are  very  small  (less  than  \  inch),  but  ex- 
tremely prolific.  In  summer  certain  females,  called  the  stem 
mothers,  bring  forth  living 
young  which  have  developed 
within  their  bodies  from 
unfertilized  eggs.  In  the  au- 
tumn fertilized  eggs  are  laid, 
which*  serve  to  carry  the 
race  through  the  winter. 
Many  aphids  are  very  de- 
structive to  vegetation.  The 
grape-phylloxera,  Phylloxera 
vastatrix  (Fig.  276),  is  the 
most  notorious;  it  punctures 
the  roots  of  grape-vines, 
causing  decay  or  "  cancer  " 
and  the  formation  of  tuber- 
cles. The  woolly  apple- 
aphis   attacks    the   roots    and        Fig.   277.  —  Order    Hemiptera.     San 

twigs   of    apple    trees ;     the  J^l  '^^''^  Sf'eSg:i; 
"  green   fly "   injures  wheat,   (After  Howard.) 


PHYLUM  ARTHROPODA 


347 


oats,  and  other  grains.  A  host  of  other  plants  are  also 
infested. 

The  scale  insects  (Family  Coccid^)  are  of  the  greatest  im- 
portance to  fruit  growers.  They  are  small  but  numerous.  The 
San  Jose  scale,  Aspidiotus  perniciosus  (Fig.  277),  was  imported 
from  its  native  home  in  Japan  or  China  to  California.  It  has 
increased  and  spread  over  a  large  part  of  this  country  and  has 
been  the  cause  of 
considerable  legis- 
lation in  an  effort 
to  control  its  dep- 
redations. The 
cottony  cushion 
scale,  Icerya  pur- 
chasi,  which  came 
near  ruining  the 
orange  groves  of 
California,  was 
successfully  con- 
trolled by  a  lady 
beetle,  Novius  car- 
dinalis  (Fig.  302), 
introduced  from 
Australia.        This 

beetle  is  the  natural  enemy  of  the  cottony  cushion  scale,  which 
is  also  a  native  of  Australia.  In  two  or  three  years  these 
beetles  checked  the  inroads  of  this  species  of  scale  insect. 

The  cicadas  (Family  Cicadid^,  Fig.  278)  are  especially  inter- 
esting, since  one  of  them,  the  seventeen-year  cicada  or  ''locust" 
{Cicada  septendecim,  Fig.  278),  lives  underground  as  a  nymph 
for  over  sixteen  years.  The  eggs  (F)  are  laid  in  slits  made  by 
the  female  in  li\dng  twigs  (E).  The  young  (A)  hatch  in  about 
six  weeks,  drop  to  the  ground,  and  burrow  beneath  the  surface 
(B).  Here  they  feed  on  juices  from  roots  and  on  humus  until 
the  summer  of  the  seventeenth  year,  when  they  emerge  from 


Fig.  278.  —  Order  Hemiptera.  Seventeen-year 
locust,  Cicada  septendecim.  A,  larva.  B,  nymph. 
C,  nymph  skin  after  emergence  of  adult.  D,  adult. 
E,  section  of  tree  showing  how  eggs  are  laid.  F,  two 
eggs  enlarged.  (From  Sedgwick's  Zoology,  after 
Riley.) 


348 


COLLEGE   ZOOLOGY 


the  ground  (C)  and  transform  into  adults  (D).  Twenty  dif- 
ferent broods  are  known  in  this  country,  and  it  is  possible  to 
foretell  approximately  when  and  where  each  swarm  will  appear. 
The  common  cicada  is  the  green  dog-day  harvest- fly,  Cicada 
tibicen.  The  males  are  provided  with  sound-making  organs, 
and,  since  these  are  lacking  in  the  female,  the  philosopher  Xen- 
archos  remarked,  "  Happy  is  the  cicada,  since  its  wife  has  no 
voice." 

(3)  Heteroptera  (The  True  Bugs,  Fig.  279).  The  first 
pair  of  wings  of  the  Heteroptera,  when  present,  are  thickened 
at  the  base.  The  jointed  beak  arises 
from  the  front  part  of  the  head. 
About  twenty-six  families  are  recog- 
nized in  this  suborder.  They  in- 
clude aquatic  forms  such  as  water- 
boatmen  (CoRisiD^),  back-swdmmers 
(NoTONECTiD^),  giant  water-bugs 
(Belostomatid^e),  water-striders  (Hy- 
DROBATID.E),  and  marsh-treaders  (Lim- 
NOBATiD^),  and  land-bugs  such  as  the 
assassin  bugs  (REDUViiDiE),  bedbugs 
(AcANTHiiD^),  chinch-bugs  (Lyg^id^, 
Fig.  279),  squash-bugs  (Coreid^),  and 
stink-bugs  (Pentatomid^).  The 
aquatic  members  of  this .  suborder  show  remarkable  adaptations 
for  life  in  the  water.  In  many  the  legs  are  modified  for  swim- 
ming, the  colors  of  the  body  are  such  as  to  conceal  them,  and 
the  methods  of  obtaining  oxygen  while  under  water  are  extremely 
interesting.  Certain  of  the  terrestrial  species  are  of  great 
economic  importance.  The  assassin  bugs  usually  prey  upon 
obnoxious  insects,  including  the  bedbug,  and  are  therefore 
beneficial  to  man;  the  chinch-bug  (Fig.  279)  is  noted  for  the 
enormous  damage  it  has  done  to  the  grain  fields  in  the 
Mississippi  Valley;  and  the  squash-bugs  infest  squash  and 
pumpkin  vines. 


Fig.  279.  —  Order  Hemip- 
TERA.  Chinch-bug,  Blissus 
leucopterus.     (After  Webster.) 


PHYLUM  ARTHROPODA 


349 


Fig.  280.  —  Order  Neuroptera.  Lace- 
wing  fly,  Chrysopa,  with  eggs  and  larva. 
(From  Packard.) 


Order  12.  Neuroptera. — Aphis-lions,  Dobson-flies,  and 
Ant-lions  (Fig.  280). — Insects  possessing  four  membranous 
wings  with  many  veins; 
biting  mouth-parts;  com- 
plete metamorphosis. 

Only  a  few  families 
have  been  left  in  the  old 
Linnean  order  Neurop- 
tera; the  rest  have  been 
taken  out  and  grouped  to- 
gether as  distinct  orders. 
The  dobson-fly,  Cory- 
dalis  cornuta,  is  a  well- 
known       representative. 

Its  larva  has  many  local  names  and  is  used  extensively  as  fish 
bait.  The  larvae  of  Hemerobius  and  of  the  lace-wing  fly, 
Chrysopa  (Fig,  280),  are  called  aphis-lions  since  they  destroy 
countless  numbers  of  aphids  by  piercing  them  with  their  sharp 
jaws  and  drinking  their  blood.  The 
eggs  of  Chrysopa  are  fastened  to  the 
top  of  upright  threads  which  are 
attached  to  a  twig  or  leaf;  they  are 
thus  protected  from  predaceous  insects, 
including  the  young  aphis-lions  them- 
selves. The  larvae  of  many  ant-lions 
live  at  the  bottom  of  pits  in  the  sand, 
where  they  capture  and  drink  the 
blood  of  any  ants  that  chance  to  slip 
down  into  the  trap. 

Order  13.     Mecoptera. — Scorpion 
Flies  and  Others  (Fig.   281). — In- 
sects possessing  four  membranous  wings 
with  numerous  veins;  head  prolonged 
into  a  beak ;  biting  mouth-parts ;  metamorphosis  complete. 
The  common  name  of  these  insects  is  due  to  the  fact  that  in 


Fig.  281.  —  Order  Mecop- 
tera. Scorpion  fly,  Panorpa 
communis,  male.  (From 
Sedgwick's  Zoology,  after 
Sharp.) 


350 


COLLEGE  ZOOLOGY 


some  species  the  abdomen  of  the  male  terminates  in  a  structure 
resembling  the  sting  of  a  scorpion.  Little  is  known  about  the 
habits  of  the  Mecoptera. 

Order  14.  Trichoptera.  —  Caddice-elies  (Fig.  282). — In- 
sects possessing  four  membranous  wings  with  many  longitudinal 

veins  and  covered 
with  hairs ;  rudi- 
mentary  mouth- 
parts;  metamorpho- 
sis complete. 

The  term  caddice- 
fly  is  derived  from 
the  case  (Fig.  282,  A) 
which  its  aquatic 
larva  builds  of 
leaves;  grass  stems, 
or  grains  of  sand  as 
a  means  of  protec- 
tion. The  larva  (B) 
can  extend  the  fore 
part  of  the  body 
and  drag  its  case 
from  place  to  place  or  can  retreat  into  its  house  for  safety. 
Thread-like  tracheal  gills  are  present  on  the  abdomen.  Each 
species  builds  a  certain  kind  of  case  which  can  be  distinguished 
from  those  built  by  other  species. 

Order  15.  Lepidoptera,  —  Butterflies,  Skippers,  and 
Moths  (Figs.  283-290).  —  Insects  with  four  membranous  wings 
covered  with  scales;  usually  sucking  mouth-parts;  meta- 
morphosis complete. 

The  members  of  this  order  are  famous  for  their  varied  and 
brilliant  colors;  these  are  produced  by  the  scales.  The  mouth- 
parts  form  a  sucking  tube  (Fig.  253)  which  may  be  five  or  six 
inches  long  and  is  coiled  under  the  head  when  not  in  use.  This 
sucking  proboscis  is  used  to  obtain  nectar  from  flowers.     The 


Fig.  282. — Order  Trichoptera.  Stages  in  the 
development  of  a  caddice-fly,  Enoicyla.  A,  case 
of  full-grown  larva.  B,  larva  and  case  enlarged. 
C,  larva  removed  from  case.  D,  wingless  adult 
female.  E,  male.  (From  the  Cambridge  Natural 
History,  after  Ritsema.) 


PHYLUM  ARTHROPOD  A  35 1 

larv^ae  of  the  Lepidoptera  are  called  caterpillars,  and  are  in 
many  cases  extremely  injurious  to  vegetation. 

Over  seven  thousand  species  of  Lepidoptera  have  been 
described  as  inhabitants  of  this  country.  These  may  be  sepa- 
rated for  convenience  into  two  suborders,  (i)  the  Rhopalocera 
or  butterflies  and  skippers,  and  (2)  the  Heterocera  or  moths. 

Suborder  i.  Rhopalocera  ^(Butterflies  and  Skippers). 
—  The  butterflies  and  skippers  may  be  distinguished  from  the 


Fig.   283.  — Order  Lepidoptera.     Monarch  butterfly,  Anosia  plexippus. 
(After  RUey.) 

moths  by  the  knoblike  swelling  near  the  end  of  the  antennae. 
The  skippers  usually  possess  in  addition  to  this  knob  a  ter- 
minal recurved  point.  Moths  do  not  possess  knobbed  antennae. 
The  members  of  the  two  suborders  differ  also  in  habits,  since  the 
butterflies  are  active  during  the  day,  whereas  the  moths  usually 
fly  at  night  or  twilight. 

Most  of  the  skippers  belong  to  the  family  Hesperid^. 
They  are  generally  small  and  comparatively  dull-colored  Rho- 
palocera that  "  skip  "  about  close  to  the  ground  from  one  plant 
to  another,  like  a  wounded  butterfly. 

The  beautiful  swallowtail  butterflies  belong  to  the  family 
Papilionid^.  They  are  characterized  by  one  to  three  "  tails  " 
projecting  backward  from  their  hind  wings.     The  tiger  swallow- 


352 


COLLEGE  ZOOLOGY 


tail,  Papilio  turnus,  is  a  well-known  species.  Its  la^^'^v  feed 
principally  on  the  wild  cherry.  A  "negro"  variety  of  the  tiger 
swallowtail  called  i^laucus  occurs  in  some  localities. 

The  family  Nympiialid^,  or  brush-footed  butterflies,  con- 
tains many  common  and  interesting  species.  The  mourning- 
cloak,  Euvanessa  antiopGy  is  one  of  the  first  to  appear  in  the 
spring.  Its  larvae  are  injurious  to  willows  and  poplars,  the 
leaves  of  which  they  devour.  The  milkweed  or  monarch 
butterfly,  Anosia  plexipf>us  (Fig.  283),  is 
abundant  about  milkweed.  It  is  distasteful 
to  birds,  and  is  therefore  immune  to  attack. 


Fig.  284.  —  Order  Lkpidoptera.     Cabbage  butterfly,  Picris  rapas. 
a,  caterpillar,     b,  chrysalis.     (From  Osborn,  after  Riley.) 

The  viceroy,  BasUarchia  archippus,  which  is  edible,  apparently 
mimics  the  monarch  so  as  to  profit  by  the  immunity  of  the 
latter. 

The  cabbage-butterfly,  Pieris  rapa  (Fig.  284),  is  a  member  of 
the  family  Pierid.^.  It  is  a  serious  pest  because  of  the  de- 
struction to  cabbages  caused  by  its  green  caterpillars.  This 
species  was  accidentally  introduced  from  Europe.  It  was  first 
discovered  at  Quebec  in  i860.  From  there  it  rapidly  spread  over 
a  large  part  of  North  America. 

Suborder  2.  Heterocera  (Moths). — The  moths  are  of 
great  importance  to  man  because  of  the  damage  done  by  some 
of  them  and  the  benefits  derived  from  others.  The  hawk-moths, 
or  humming-bird  moths  (SPHiNGiDiE),  have  a  thick  body  and 
narrow,  pointed  wings,  and,  when  hovering  before  a  petunia  or 


PHYMJM    Ak'niROI'ODA 


353 


[)nmrosc,  resemble  a  liuninjin^^-binl.  The  larva;  live  on  the 
leaves  of  tomato  and  tobacco  i>lants,  Virginia  creeper,  and  many 
others;  they  are  usually  very  large.  The  family  Arctiid^ 
contains  the  fall-we})worm,  Ilyphantria  cunea,  the  larvae  of 
which  live  together  in  a  web 
and  eat  the  leaves  of  many 
kinds  of  trees  and  shrubs. 
The    white-spotted    tussock- 


A  Ji  C 

Fig.  285,  —  Order  Lkpiooptkua.     (Jyiwyrnoth,  I'orthetr.ia  dispar 
B,  larva.     C,  pupa.     (From  Osborn,  after  Howard.) 


A,  female. 


moth,  whose  larvae  feed  on  the  leaves  of  trees  and  are  often  very 
troublesome,  belongs  to  the  family  Lymantkid>*:.  Another 
important  member  of  this  family  is  the  gypsy-moth,  Porthelria 
dispar  (Fig.  285).    The  gypsy-moth  was  imix^rted  from  Europe. 


Fig.  286. — Order  Lepidoptera.     Silkworm,  jBow^jc  won.     A,  caterpillar. 
B,  cocoon.     C,  adult  female  moth.     (From  Shipley  and  MacBridc.) 


Its  caterpillars  devour  leaves  and  have  killed  many  of  the  finest 
shade  trees  in  certain  parts  of  Massachusetts. 

A  number  of  large  common  moths  are  placed  in  the  family 
BoMHYCii)^: ;  for  example,  the  cccropia,  Plalysamia  cecropidy 
the  giant    silkworm  moth,    Tdca    pnlyphemus,  the   luna  moth, 

2   A 


354 


COLLEGE  ZOOLOGY 


TropcBa  luna,   the   "  tent-caterpillar,"    Clisiocampa  americana, 
and   the  silkworm  moth,  Bombyx  mori.     The   silkworm  moth 

(Fig.  286,  C)  is  thoroughly 
domesticated  and,  so  far 
as  is  known,  does  not  occur 
in  a  wild  state.  The  silk 
industry  originated  in 
China  many  centuries  B.C. 
It  did  not  become  very 
important  in  this  country 
until  the  nineteenth 
century.  There  are  now 
about  a  hundred  million 
dollars  invested  in  the  silk 

Fig.  287.  —  Order  Lepidoptera.     Army-  •    j      .    •           r    4.1,       tt    v   j 

worm,  Hcliophila  unipuncta.     a,  adult,     b.  mdustnes    of    the     United 

larva,  with  eggs  of  a  parasitic  fly  (tachinid)  States.      The      moths     lay 

on    back,     c,    pupa    or    chrysalis.     (From  ,i     •                                 i    ii. 

Webster,  Yearbook  Dep't  Agric,   1908.)  their     eggS     On      cloth     Or 

paper  provided  for  them. 
The  larvae  (Fig.  286,  A)  are  fed  principally  on  mulberry  leaves, 
and  when  about  forty  days  old  spin  a  cocoon  (B)  of  a  single 
continuous  thread  averaging  over  a  thousand  feet  long.  In 
the  cocoon  the  larva  pupates. 
Silk  is  obtained  by  killing  the 
pupa  with  heat  or  boiling  water, 
then  clearing  away  the  loose  out- 
side floss,  and  unwinding  the 
thread. 

Among  the  important  moths 
of  the  family  N0CTUID.E  are  the 
army- worm,  Heliophila  uni- 
puncta, the  cotton-worm,  Aletia 
argillacea,  and  the  boll-worm, 
Heliothis  armiger.  The  army- 
worms  (Fig.  287)  are  striped  b,  female.  c,  larva.  d,  eggs- 
"^     ^  I  ^  t^  natural  size  and    enlarged.     (From 

caterpillars  that  feed  on  growing    circ.  9,  Bur.  Ent.,  U.  S.  Dep't  Agric.) 


Fig.   288.  —  Order  Lepidoptera. 
Spring      canker-worm.        a,     male. 


PHYLUM   ARTHROPODA 


355 


Fig.  289.  —  Order  Lepidoptera.  Codlin-moth, 
Carpocapsa  pomonella.  a,  adult,  b,  larva  in  an 
apple,  c,  pupa  or  chrysalis.  (From  Farmer's  Bui. 
283,  U.  S.  Dep't  Agric.) 


wheat,  oats,  corn,  timothy,  blue  grass,  and  other  plants.  They  mi- 
grate from  one  field  to  another  in  large  numbers,  hence  their  name. 
The  tachina  flies 
parasitize  many  of 
them  and  fungus 
diseases  attack 
others,  so  that 
they  are  partially 
held  in  check  by 
their  natural  ene- 
mies. The  cotton- 
worm  eats  the 
leaves  of  the  cot- 
ton plant.  The 
boll- worm  is 
widely  distributed  and  feeds  not  only  upon  the  cotton  boll  but 
also  upon  corn,  tomatoes,  tobacco,  and  other  plants. 

The  larvae  of  the  Geometrid^  are  called  measuring  worms 
because  of  their  looping  method  of  locomotion.  One  of  the 
most  important  species  is  the  spring  canker-worm,  Paleacrita 
vernata  (Fig.  288),  the  larvae  of  which  eat  the  foliage  of  fruit 
trees  in  various  parts  of  the  country. 

The  codlin-moth,  or  apple- worm  (Fig.  289),  Carpocapsa 
pomonella  (Family  Tortricid^),  is  the  foremost  apple  pest  in 

this  country.  The  annual 
loss  due  to  this  moth  is 
estimated  at  $11,400,000 
(Simpson).  The  eggs  are 
laid  upon  the  young  fruit, 
and  the  larvae  eat  their 
way  into  the  core. 

The  family  Tineid^ 

Fig.  290.  — Order  Lepidoptera.  Clothes-  Contains  a  large  num- 
moth,  Tinea  pdlioneUa.    a   adult,    b,  larva.    ^^^   ^f  ^^^]^   moths. 

c,  larva  in  case.     (From  Riley,  in  Circ.  36,  -^ 

Bur.  Ent.,  u.  s.  Dep't  Agric.)  The   clothes-moth,    Tinea 


356  COLLEGE  ZOOLOGY 

pellionella  (Fig.  290),  injures  animal  textiles  of  all  kinds.  Its 
larvae  feed  on  fur,  feathers,  woolen  fabrics,  etc.  The  larvae 
of  the  grain  moth,  Gelechia  cerealella,  bore  into  kernels  of 
wheat,  rye,  and  corn. 

Order  16.  Diptera.  —  Flies  (Figs.  291-295).  —  Insects  with 
two  wings  attached  to  the  meso thorax;  the  meta thorax  bears 
knobbed  threads,  the  halteres;  sucking  mouth-parts;  meta- 
morphosis complete. 

This  is  one  of  the  largest  orders  of  insects,  there  being  about 
seven  thousand  known  species  in  North  America.  These  may 
be  grouped  as  follows: 

Suborder  i.    Diptera  genuina  (true  flies). 
Section  i.     Nematocera  (long-horned  flies). 
Section  2.     Brachycera  (short-horned  flies). 

Suborder  2.     Pupipara  (ticks  and  lice). 

The  Nematocera  include  the  mosquitoes,  crane  flies,  gall- 
gnats,  midges,  and  black  flies. 

The  mosquitoes  (Culicid^)  have  an  interesting  life-history. 
The  eggs  are  laid  on  the  surface  of  the  water  in  a  raft-like  mass 
(Fig.  291,  b)  or  singly.  The  larvae  Uve  in  the  water  and  are 
known  as  wrigglers  (Fig.  291,  c);  they  have  an  air  tube  on  the 
abdomen  which  is  thrust  through  the  surface  film  of  water. 
The  pupa  is  likewise  aquatic.  The  adult  male  differs  from  the 
female  (Fig.  291,  a)  in  the  structure  of  the  antennae  and  in  feed- 
ing habits.  Only  the  females  suck  blood;  the  males,  if  they 
eat  at  ah,  probably  feed  on  nectar.  It  has  been  proved  by 
experiments  that  mosquitoes  of  the  genus  Anopheles  transmit 
human  malaria  (see  Chap.  II),  and  that  individuals  of  the 
genus  Stegomyia  transmit  yellow  fever  germs.  The  larvae  and 
pupae  of  mosquitoes  may  be  destroyed  by  draining  pools  and 
swamps  or  by  covering  the  water  with  a  thin  layer  of  oil,  which 
prevents  them  from  obtaining  air. 

The  crane  flies  (Tipulid^e)  look  like  large  mosquitoes.  The 
gall-gnats  (Cecidomyiid^e)  are  terrestrial  during  their  entire 
lives.     Their  common  name  has  been  given  to  them  because 


PHYLUM  ARTHROPODA 


357 


Fig.  291.  —  Order  Diptera.  Mosquito,  C-ulex  pungens.  a,  adult  female. 
b,  egg  mass  on  surface  of  water,  c,  young  hanging  from  surface  of  water. 
(From  Howard,  Bui.  25,  Bur.  Ent.,  U.  S.  Dep't  Agric.) 


many  lay  eggs  in  plant  tissue  whose  larvae  when  hatched  cause  an 

abnormal  growth  called  a  gall,  e.g.  the  pine-cone  willowgall.    One 

gall-gnat,  the  Hessian  fly,  Cecidomyia  destructor  (Fig.  292),  causes 

a  loss  of  about  $10,000,000  annually  to  the  wheat  crop  in  this 

country.      Several  species  of  this 

family  are  paedogenetic  (see  p.  80). 

The  midges  (Chironomid^)  are 

harmless  little  insects  resembling 

mosquitoes.     The  larvae  of  some 

of  them  are  the  blood-red  Httle 

worms  found  in  water.     The  black 

flies    (S1MULIID.E)    are    notorious 

blood-sucking  pests  and  the  special 

torment  of  hunters,  fishermen,  and 

campers.     Their  larvae  live  in  swift       ,.  r^  j        T^ 

^  ,      .  Fig.    292.  —  Order      Diptera. 

streams  clinging  to  the  surfaces  of     Hessian  fly,  Cecidomyia  destructor. 

rocks,  and  the  adults  are  therefore    *'^f^^,;  \P"Pf-  ^^^^^f^  ^^^r,^.^" 

port,  after  Standard  Natural  His- 

found  m  the  vicinity  of  water.  tory.) 


358 


COLLEGE  ZOOLOGY 


The  Brachycera  include  the  horse-flies,  bee-flies,  house- 
flies,  bot-flies,  and  flower- flies.  The  horse-flies  (Tabanid^) 
are  well-known  pests  of  cattle  and  horses  and  often  man.  The 
female  sucks  blood,  but  the  male  lives  on  nectar.  The  larvae 
live  in  the  water  or  in  the  earth,  where  they  feed  on  small  ani- 
mals. The  bee-flies  (BoMBYLiiDiE)  look  somewhat  like  true 
bees.  They  feed  on  nectar  as  adults,  but  the  larvae  are  car- 
nivorous, living  on  the  young  of  bees,  wasps,  and  grasshoppers. 

The  house-flies  belong  to  a  family  (Muscid^)  which  contains 
about  a  third  of  all  the  known  Diptera.    The  house-fly,  Musca 


Fig.  293.  —  Order  Diptera. 
House-fly,  Musca  domestica. 
(From  Howard,  Circ.  71,  Bur. 
Ent.,  U.  S.  Dep't  Agric.) 


Fig.  294.  —  Order  Diptera.  Horse 
bot-fly,  Gastrophilus  equi.  a,  larva. 
b,  adult.  (From  Sedgwick's  Zoology, 
after  Brauer.) 


domestica  (Fig.  293) ,  is  dangerous,  since  it  carries  disease  germs, 
such  as  typhoid  and  tuberculosis,  from  place  to  place.  Its  eggs 
are  laid  principally  in  horse  manure  and  the  larvae  are  called 
maggots.  The  adults  can  be  controlled  by  keeping  the  horse 
manure  and  other  filth  under  cover.  The  flesh-flies  deposit 
living  young  in  meat  or  in  open  wounds.  The  blow-fly  lays  its 
eggs  on  meat,  which  is  then  said  to  be  "blown."  Thetachina- 
flies  are  beneficial,  since  their  larvae  are  parasitic  upon  cater- 
pillars  (Fig.    287),  often   exterminating  vast  hordes  of  army- 


PHYLUM    ARTHROPODA 


359 


Fig.  295.  —  Order 
DiPTERA.  Sheep-tick, 
Me  lophagus  ovinus. 
(From  Sedgwick's 
Zoology ) 


worms  and  other  pests.     The  fruit-flies  are  abundant  flies  and 

easily  reared. 
The  bot-flies  (CEstrid^)  are  responsible  for  large  losses  every 

year  because  of  their  attacks  on  domestic  animals.     The  horse 

bot-fly,  Gastrophilus  egui  (Fig.  294),  fastens 

her  eggs  to  the  hair  on  the  legs  or  shoulders  of 

horses.     The  larv^ae,  which  are  licked  off  and 

swallowed,  attach  themselves  to  the  lining  of 

the  stomach,  where  they  Uve  until  ready  to 

pupate.     They  then  pass  out  of  the  alimen- 
tary canal.     Other  common  members  of  this 

family  are  the  ox-warble j  the  larvae  of  which 

ruin  the  hides  of  cattle  by  boring  through 

the  skin,  the  sheep  bot-fly^  which   lives  in 

the  nostrils  of  sheep,  and  the  rabbit  bot-fly. 

The  flower-flies  (Syrphid^)  live  on  nectar  and   pollen   and 

are  therefore  found  near  flowers.  The  larvae  feed  on  other  in- 
sects or  on  vegetable  matter. 
The  drone- fly,  Eris talis  tenax, 
resembles  a  drone  honey-bee. 
The  suborder  Pupipara 
contains  parasitic  insects,  in- 
cluding bird,  sheep,  and  horse 
ticks,  and  bee-lice.  The 
sheep-tick,  Melophagus  ovinus 
(Fig.  295),  and  the  horse-tick, 
Hippobosca  equina,  are  com- 
mon species. 

Order  17.  Siphonaptera. 
— Fleas  (Fig.  296). — Degen- 
erate insects  without  wings; 
sucking  mouth-parts;  meta- 
morphosis complete. 
The  fleas  live  among  the  hairs  or  feathers  of  domestic  and 

wild  mammals  and  birds.    Their  bodies  are  laterally  compressed, 


■/ 


Fig.  296.  —  Order  Siphonaptera.  Cat 
and  dog  flea,  Ctenocephalus  canis.  a,  egg. 
b,  larva  in  cocoon,  c,  pupa,  d,  adult. 
(From  Howard,  Circ.  108,  Bur.  Ent., 
U.  S.  Dep't  Agric.) 


360  COLLEGE  ZOOLOGY 

their  heads  are  very  small,  and  their  legs  are  fitted  for  leaping. 
The  larvae  feed  on  decaying  animal  and  vegetable  matter. 
The  cat  and  dog  flea,  Ctenocephalus  cams  (Fig.  296),  is  the  most 
common  species.  It  does  not  restrict  its  attacks  to  the  dog, 
however,  but  also  visits  man.  The  human  flea,  Pulex  irritans,  is 
found  all  over  the  world.  The  rat  flea,  Lcemopsylla  cheopus, 
is  of  considerable  importance,  since  it  seems  to  be  able  to  trans- 
mit the  bubonic  plague  from  rats  to  man.  The  jigger  or  chigoe 
flea,  Sarcopsylla  penetrans,  burrows  into  the  skin  of  man  and 
often  causes  considerable  trouble. 

Order  18.  Coleoptera.  —  Beetles  (Figs.  297-304). — In- 
sects with  four  wings,  the  fore-wings  sheath-like  (elytra)  and 
covering  the  membranous  hind  wings;  biting  mouth-parts; 
metamorphosis  complete. 

This  order  contains  a  great  number  of  species;  there  are 
nearly  twelve  thousand  known  in  North  America,  north  of 
Mexico.  For  convenience  they  have  been  grouped  into  eight 
suborders. 

Suborder  i.  Adephaga.  (Carnivorous  Beetles,  Fig. 
297.)  —  The  four  principal  families  of    carnivorous  beetles  are 

the  tiger-beetles  (Cicin- 
delid^,  Fig.  297),  pre- 
daceous  ground  beetles 
(Carabid^)  ,  predaceous 
diving-beetles  (Dytis- 
ciD^),  and  whirligig- 
beetles  (Gyrinid^e).    The 

Fig.  297.  -  Order  Coleoptera.  Tiger-  ^^^^  ^^^  families  are  ter- 
beetles,    Cicindelid^.       (From    Davenport, 

after  Packard.)  restrial;  they  remam  on 

the  ground  most  of  the 
time,  where  they  are  busily  engaged  in  capturing  other  insects 
for  food.  The  whirligig-  and  diving-beetles  are  aquatic  and  are 
modified  for  Hfe  in  the  water.  In  general  it  may  be  said  that 
the  carnivorous  beetles  and  other  carnivorous  insects  are  bene- 
ficial, since  they  usually  destroy  insects  harmful  to  man. 


PHYLUM   ARTHROPODA 


361 


Order 
Car- 


They  comprise  the   hj^^'^'^^)^    Natural 


Suborder  2.  Clavicornia.  (Club-horned  Beetles, 
Fig.  298.)  —  The  club-horned  beetles  have  clubbed  antennae. 
They  have  little  in  common ;  some  are 
aquatic,  others  terrestrial  ;  some  are  pre- 
daceous,  and  therefore  beneficial;  others 
herbivorous,  and  consequently  harmful;  and 
a  few  feed  on  decaying  organic  matter. 
Some  of  the  commoner  species  are  known  ^ 
as  w^ater-scavenger  beetles  (Hydrophilid^), 
rove-beetles  (Staphylinidae),  grain  beetles 
(CucujiD^),  burying-beetles  (Silphid^,  Fig. 
298),  and  larder-beetles  (Dermestid^).  Coleoptera 

Suborder  3.  Serricornia.   (Saw-horned   "on-beetie,  Siipha 

^  ^  amertcana.         (From 

Beetles,  Fig.  299.)  — The  saw-horned  beetles  Davenport,  after 
have  saw-like  antennae 
metallic  wood  borers  (Buprestid^)  which 
injure  fruit,  shade,  and  forest  trees;  the  click-beetles  (ELATERiDiE, 
Fig.  299),  so  called  because  when  laid  on  their  backs  they  are 
able  to  spring  up  with  a  click;  the  death-watch  beetles  (Ptinid^), 

some  of  which  make  a  ticking 
sound  against  the  wood  in  which 
they  burrow;  the  fireflies  and 
soldier-beetles  (Lampyrid^)  ,  the 
former  nocturnal  and  occasion- 
ally luminous,  the  latter  diur- 
nal and  predaceous ;  and  the 
checkered  beetles  (Clerid^),  some  of  which  devour  the  larvae 
of  wood-boring  insects. 

Suborder  4.  Lamellicornia.  (Blade-horned  Beetles, 
Fig.  300.)  The  blade-horned  beetles  have  antennae  whose 
terminal  segments  form  flat  teeth  or  lamellae.  The  stag- 
beetles  (LucANiD^)  have  received  their  name  because  of  the 
peculiar  antler-like  processes  of  the  males  of  certain  species. 
The  leaf  chafers  and  scavenger-beetles  (Scarab ^id^e)  have 
very  different  habits,  although  they  belong  to  one  family.     The 


Fig.  299.  - 
Click-beetle. 


Order  Coleoptera. 
(From  Davenport.) 


362 


COLLEGE  ZOOLOGY 


Fig.  300.  —  Order  Cole- 
OPTERA.  Sacred  beetle  of 
the  Egyptians,  Scarabeus 
sacer.  (From  Sedgwick's 
Zoology,  after  Sharp.) 


scavenger-beetles  eat  or  bury  decaying  matter  and  are  therefore 
beneficial  The  tumble-bugs  make  balls  of  dung  in  which  an 
egg  is  laid;  the  larva  feeds  on  the  ball. 
To  this  group  belongs  the  Sacred  Scara- 
beus of  the  Egyptians  (Fig.  300).  The 
leaf'  chafers  are  injurious.  The  adults 
feed  on  leaves,  pollen,  and  flower-petals. 
The  common  June-bug,  Lachno sterna 
fusca,  the  obnoxious  rose-chafer,  Macro- 
dactylus  subspinosus,  and  the  rhinoceros- 
beetles,  Dynastes,  belong  to  this  group. 
One  of  the  latter,  D.  hercules,  found  in 
the  West  Indies,  is  six  inches  long. 

Suborder  5.  Phytophaga.  (Plant- 
eating  Beetles,  Fig.  301.)  —  The 
plant-eating  beetles  include  the  leaf- 
beetles  (CHRYSOMELiDyE) ,  the  pea-  and 
bean- weevils  (BRUCHiDiE),  and  the 
long-horn  beetles  (Cerambycid^).  The  potato-beetle,  Lep- 
tinotarsa  lo-lineata  (Fig.  301),  belongs  to  the  first  family.  It 
migrated  up  from  Mexico  into  Colorado  and  thence  east  and 
west  until  it  became  an  important 
pest.  The  elm  leaf  beetle,  Galeru- 
cella  luteola,  is  another  injurious 
chrysomelid  beetle.  It  has  de- 
stroyed a  great  number  of  valuable 
elm  trees  in  Massachusetts  and 
neighboring  states. 

The  larvae  of  the  pea-  and  bean- 
weevils  burrow  into  peas  and  beans, 
making  them  unfit  either  for  food 
or  seed. 

The  larvae  of  the  long-horn  beetles       Fig.  301.  —  Order    Coleop- 

•L  .  1         J  ,1        tera.     Potato-beetle,    Leptino- 

burrow  m  wood  and  are  among   the     ^^^^^  decemlineata.      (From  the 

most    destructive    enemies    of    trees.     Cambridge  Natural  History.) 


PHYLUM   ARTHROPODA 


363 


Some  of  the  worst 
pests  are  the  locust 
borer,  Cyllene  robinice, 
the  apple  tree  borer, 
Saperda  Candida,  and 
the  sugar  maple  borer, 
Plagionotus  speciosus. 
A  common  species, 
Tetraopes  tetraophthal- 
mus,  is  found  on  milk- 
weed. 

Suborder  6.  Tri- 
MERA.  (Ladybird 
Beetles,  Fig.  302.)  — 

The       COCCINELLID^, 

or    ladybird    beetles, 


CO 

Fig.  302.  —  Order  Coleoptera.  Novius  cardi- 
nalis,  Australian  ladybird  beetle,  feeding  on  the 
fluted  scale,  Icerya  purchasi.  a,  ladybird  larvae 
feeding  on  adult  female  and  egg  sac ;  b,  pupa ; 
c,  adult  ladybird ;  d,  orange  twig,  showing  scale 
and  ladybirds  —  natural  size.      (From  Marlatt.) 


are  predaceous,  both 
as  larvae  and  adults, 
feeding  largely  on  plant-lice  and  scale-insects.  They  are  conse- 
quently beneficial  since  they  help  control  these  pests  (see  p.  347). 
Suborder  7.  Heteromera.  (Darkling,  Blister-  and  Oil- 
Beetles,  Fig.  303.)  — The  Heteromera  contains  the  darkling 
ground-beetles  (Tenebrionid^),  one  of  which,  the  meal-worm, 

Tenebrio  molitor  (Fig.  303), 
is  quite  common  in  mills 
and  grocery  stores  and  is 
used  as  food  for  cage 
birds.  This  group  also 
includes  the  blister-  and 
oil-beetles  (Meloid^e)  ; 
some  of  these  when  dried 
and  pulverized  have  a 
Fig.  303.  — Order  Coleoptera.  Meal-  blistering  effect  when 
joxmTcnehrio  molitor  k,\^rv^.  B  pupa  applied  tO  the  human 
C,  adult.  (From  the  Cambridge  Natural  ^'^ 
History.)  skin. 


364 


COLLEGE  ZOOLOGY 


Suborder  8.  Rhynchophora.  (Snout-beetles,  Fig.  304.) 
—  The  Rhynchophora  are  the  curculios,  weevils,  bill-bugs,  and 
snout-beetles.  The  front  of  the  head  is  prolonged  into  a  beak 
or  snout,  with  the  mouth-parts  at  the  end.     Weevils  (Fig.  304,  A) 

attack  many  varieties  of 
fruits,  nuts,  and  grain. 
The  bark-beetles  (Scoly- 
TiD^)  are  the  most  de- 
structive of  all  insects 
to  forest  trees,  their 
depredations  reaching 
a  total  of  probably 
$100,000,000  annually. 
The  genera  Dendroc- 
tonus  (Fig.  304,  B)  and 
Tomicus  are  the  most 


Fig.  304-  —  Order  Coleoptera.     A,  cotton-    notorious 
boll  weevil.     B,  southern  pine  beetle,  Dendroc- 
tonus  frontalis.     {A,  from    Farmer's   Bui.   189; 
B,   from    Hopkins,    Bui.    83,    Bur.    Ent.,  U.  S. 
Dep't  Agric.) 


Order  19.  Hymenop- 
tera.  —  Saw-flies, 
Gall-flies,  Ichneu- 
mon-flies, Ants,  Bees,  Wasps  (Figs.  305-312).  —  Insects 
possessing  four  membranous  wings  with  few  veins;  first  ab- 
dominal segment  fused  or  partly  fused  with  thorax;  mouth-parts 
both  mandibulate  and  suctorial;  female  with  an  ovipositor; 
metamorphosis  complete. 

There  are  about  seventy-five  hundred  species  of  Hymenop- 
tera  inhabiting  North  America.  They  may  be  grouped  into 
suborders,  superfamilies,  families,  subfamilies,  etc.,  but  because 
of  the  limited  space  that  can  be  devoted  to  them-  in  this  book, 
only  a  few  of  the  most  important  families  will  be  considered; 
these  are  the  saw-flies  (Tenthredinid^),  the  chalcid- flies 
(Chalcidid^),  the  gall-flies  (Cynipid^),  the  ichneumon- flies 
(IcHNEUMONiD^),  the  bces  (Apid^),  the  solitary  wasps  (Eu- 
MENiDiE),  the  social  wasps  (Vespid^),  the  digger-wasps 
(Sphegid^),  and  the  ants  (Formicid^). 


PHYLUM  ARTHROPODA 


365 


The  saw-flies  (Tenthredinid^,  Fig.  305)  are   not  generally 
noticed  as  adults,  but  their  larvae,  which  feed  on  the  leaves  of 


Fig.  305.  —  Order  Hymenoptera.  Saw-fly,  Nematus  venlricosus.  a,  adult 
female ;  b,  larvae  (currant  worms) ;  c,  adult  male.  (From  Report  State  Ento- 
mologist of  Minnesota.) 

the  rose,  currant,  pear,  willow,  and  larch,  are  only  too  well  known. 
The  eggs  are  usually  laid  in  slits  made  in  plant  tissue  by  the 
saw-like  ovipositor  of  the  female.  The  larva;  possess  usually 
from  six  to  eight  pairs  of  abdominal  legs  and  can  thus  be  dis- 
tinguished from  the  larvae 
of  Lepidoptera,  which 
have  not  more  than  five 
pairs.  Some  adult  saw- 
flies  lay  eggs  which  develop 
parthenogenetically. 

The  chalcid-flies  (Chal- 
ciDiD^,  Fig.  306)  are 
minute  parasites  which 
perform  a  service  of  in- 
estimable  value    to   man, 

since  they  attack  the  eggs,  caterpillars,  and  adults  of  many 
injurious  insects.  The  eggs  are  laid  on  or  in  the  host  and 
the  larvae  slowly  devour  its  soft  parts.     One  species,  Blasto- 


FiG.  306.  —  Order  Hymenoptera.  Chal- 
cid-fly,  Prospalta  murlfeldtii.  (From  Insect 
Life.) 


366 


COLLEGE  ZOOLOGY 


phaga  grossorum,  is   held   responsible   for   the  fertilization  of 
the  fig. 

The  gall-flies  (Cynipid^,  Fig.  307)  are  small,  dull-colored 
insects  possessing  a  long  ovipositor  with  which  eggs  are  laid  in 
plant  tissue.  In  some  w^ay  the  plant  is  stimulated  so  that  an 
abnormal  growth,  called  a  gall,  is  produced.     The  young  gall- 


FiG.  307.  —  Order  Hymenoptera.  A,  gall-fly,  Rhoditcs  rosce,  female. 
B,  galls  produced  by  a  bug.  (A,  from  the  Cambridge  Natural  History; 
B,  from  Davenport,  after  Kerner.) 


fly  is  protected  by  the  surrounding  tissue.     Many  species  are 
parthenogenetic,  and  only  females  are  known. 

The  hees  {Avidm)  comprise  a  large  family,  of  which  the  honey- 
bee is  the  best-known  example.  All  grades  of  social  life  are 
exhibited  by  bees.  The  leaf-cutter,  Megachile  acuta,  is  a  solitary 
species;  she  lays  her  eggs  in  leaf -lined  cavities  in  wood,  places 
pollen  and  nectar  in  the  cavities  for  the  larvae  to  feed  on, 
and  then  flies  away  never  to  return.  The  carpenter  bee, 
Ceratina  dupla,  is  also  a  solitary  bee,  but  she  watches  her 
young  until  they  mature.  Certain  mining  bees,  e.g.  Andrena, 
lay  eggs  in  burrows  in  the  ground  (Fig.  309,  B).  They  are 
solitary  bees  but  often  build  their  tunnels  close  together, 
i.e.   they  have  a  tendency  toward   a   gregarious   habit.     The 


PHYLUM  ARTHROPODA 


367 


Fig.  308.  —  Order  Hymenoptera.  Ich- 
neumon-fly, Thalessa  lunator,  laying  eggs 
(oviposition).  (From  Sedgwick's  Zoology, 
after  Riley.) 


females  of  other  mining 
bees,  e.g.  Halidus,  band 
together  and  use  a  single 
main  burrow  from  which 
the  individual  channels 
branch  off  (Fig.  309,  A). 
These  bees  therefore  have 
a  tendency  toward  com- 
munity life.  The  bumble- 
bees, Bombus,  live  in 
colonies  during  the  sum- 
mer, but  these  colonies 
are  temporary,  since  all 
members  but  the  young 
queens  perish  in  the 
autumn.  And  finally  the 
honey-bees,  as  we  have 
seen,  are  banded  together 
in  permanent  colonies  and  have  a  very  complex  social  life. 
The  solitary  wasps  (Eumenid.^)  are  miners,  carpenters,  or 
masons,  i.e.  they  dig  tunnels  in  the  earth,  excavate  cavities 
in  wood,  or  build  mud-nests.     Like  the  solitary  bees^  the  Eu- 

menidae  provision  their  nests, 
lay  their  eggs,  and  then  fly 
away,  leaving  their  young  to 
shift  for  themselves. 

Many  of  the  digger-wasps 
belong  to  the  family  Sphe- 
GiDiE.  The  mud-daubers 
are  common  species.  They 
attach  their  mud-nests  to  the 
ceilings  of  buildings  or  to  the 
lower  surface  of  stones,  and 
provision  them  with  spiders. 
The  digger-wasps  of  the  West 


Fig.  309.  —  Diagrams  of  nest  burrows 
of  short-tongued  mining  bees.  A,  nest  of 
Halidus.  B,  nest  of  Andrena.  (From 
Hegner,  after  Kellogg.) 


368 


COLLEGE  ZOOLOGY 


(genus  Ammophila,  Fig.  310) 
paralyze  caterpillars  with  their 
sting  and  place  them  in  their 
burrows  in  the  ground  for  the 
larvae  to  live  on.  The  burrows 
are  then  carefully  filled  up  with 
earth  and  the  top  made  level 
with  the  surrounding  surface. 

The  social  wasps  (Vespid^) 
live  in  temporary  colonies  con- 
taining females,  males,  and  sexu- 
ally undeveloped  females,  called 
workers.     They  do  not  leave  their 

Fig.  310. -Order  Hymenoptera.  ^^  jj^g  ^  food  Stored  up 

Solitary    digger-wasp,    Ammophtla,    -'  ^  ^  r 

putting  inchworm  into  nest  burrow,   for  them,  but  care  for  them  con- 
(From  Bailey  and   Coleman,  after  stantly.     The  Commonest  genera 

are  Polistes  and  Vespa.  The  hor- 
net, Polistes  (Fig.  311),  builds  a  nest  of  a  single  layer  of  cells 
made  out  of  wood-pulp.  This  single  comb  nest  is  hung  by  a 
stalk  under  the  eaves  or  to  the  ceiling  of  an  outbuilding,  or 


311.  — Hornet  and  nest,  Polistes  tepidus. 
(From  Shipley  and  MacBride.) 


porch.     Only  the  females  survive  the  winter,  and  new  colonies 
must  therefore  be  established  each  spring.     The  yellow-jacket, 


PHYLUM  ARTHROPODA 


369 


Vespa,  builds  a  more  elaborate  nest  than  that  of  Polistes.  It 
consists  of  a  series  of  combs  one  above  the  other,  and  is  sur- 
rounded by  a  paper  covering  with  an  entrance  near  the  pointed 
lower  end. 

The  ants  (Formicid^)  constitute  in  many  ways  the  most 
remarkable  group  of  insects  in  the  world.  Their  adaptations  for 
the  complex  social  life  that  the^  lead  are  very  wonderful.  A 
colony,  as  in  the  social  bees  and  wasps,  contains  a  queen,  males, 
and  workers.  The  workers  may  be  modified  as  large  or  small 
workers,  or  as  soldiers.    Ants  usually  live  in  tunnels  in  thegroimd, 


Fig.  312.  —  Honey  ants  and  leaf-cutting  ants. 
(From  Brehm.) 


or  in  wood,  or  in  the  hollow  stems  of  plants.  Beetles  and  other 
insects  live  in  ants'  nests.  The  honey-ant,  Myrmecocystus  (Fig. 
312,  i)  is  a  peculiar  form.  Some  of  the  workers  cling  to  the  roof 
of  the  mound-like  nests  and  serve  as  reservoirs  for  the  storing  of 
a  sort  of  honey  until  it  is  needed  by  the  colony.  The  leaf-cutter 
ants  (Fig.  312,  2)  of  the  genus  Atta  {(Ecodoma)  have  a  peculiar 
method  of  securing  food.  Certain  workers  cut  out  pieces  of 
leaves  and  carry  them  to  the  nest,  where  the  other  workers  pack 
them  into  balls  on  which  they  cultivate  a  fungus,  Rozites  gongy- 
lophora.  The  ants  regulate  the  growth  of  this  fungus  in  such 
a  way  that  it  produces  white  masses  which  serve  as  food  for  the 
colony. 


2  B 


370 


COLLEGE  ZOOLOGY 


d.    The  Economic  Importance  of  Insects 

The  economic  importance  of  certain  insects  has  been  em- 
phasized during  our  discussion  of  the  orders  of  insects.  A  few 
species  of  insects  are  of  considerable  value  to  man.  For  example, 
the  honey-bee  produces  enormous  quantities  of  both  honey  and 
wax;  the  silkworm  suppUes  us  with  delicate  silk  threads;  the 
bees  and  many  other  insects  cross-fertiHze  flowers;  the  bodies 
of  the  scale  insect,  Coccus  cacti,  are  known  as  cochineal;  pre- 
daceous  species  usually  prey  upon  injurious  insects;  and  many 
parasitic  species  attack  destructive  caterpillars. 

On  the  other  hand,  the  injurious  insects  are  numerous  and  im- 
portant. Some  of  them  are  responsible  for  the  transmission  of 
certain  diseases.  For  example,  the  house-fly  carries  the  germs 
of  typhoid,  tuberculosis,  cholera,  and  many  other  diseases  on  its 

TABLE  XIII 

ANNUAL  LOSSES  DUE  TO  INSECT  PESTS  OF  THE  UNITED  STATES 


Product 

Value 

Percentage 
OF  Loss 

Amount  of  Loss 

Cereals      .... 

$2,000,000,000 

10 

$200,000,000 

Hay      .     . 

530,000,000 

10 

53,000,000 

Cotton      . 

600,000,000 

10 

60,000,000 

Tobacco    . 

53,000,000 

10 

5,300,000 

Truck  crops 

265,000,000 

20 

53,000,000 

Sugar    .     . 

50,000,000 

10 

5,000,000 

Fruits   .     . 

135,000,000 

20 

27,000,000 

Farm  forests 

110,000,000 

10 

1 1 ,000,000 

Miscellaneous  crops 

58,000,000 

10 

5,800,000 

Animal  products     . 

1,750,000,000 

10 

175,000,000 

Total      .     .     . 

5,551,000,000 

595,100,000 

Natural  forests  and 

forest  products    . 

100,000,000 

Products  in  storage 

100,000,000 

Grand  to 

tal 

795,100,000 

PHYLUM   ARTHROPOD  A  37 1 

legs,  proboscis,  and  body;  the  anopheles  mosquito  transmits 
the  malaria  germ;  the  stegomyia  mosquito  transmits  the  yellow 
fever  germ ;  the  rat  flea  carries  plague  germs  ;  the  body-louse 
transmits  relapsing  fever;  and  the  tsetse- fly  is  responsible  for 
sleeping-sickness. 

Millions  of  dollars  are  lost  every  year  because  of  the  attacks 
of  insects  upon  domestic  animals.  Among  these  insects  are  the 
blood-sucking  gnats,  buffalo-gnats,  horse-flies,  gadflies,  bot-flies, 
horn-flies,  flesh-flies,  ticks,  fleas,  sucking  lice,  and  bird-lice. 

Even  more  enormous  are  the  losses  due  to  insects  that  eat  the 
leaves  of  plants,  bore  into  their  stems,  suck  their  juices,  or  de- 
stroy their  fruits.  Table  XIII  presents  a  conservative  estimate 
of  these  losses.    (Marlatt.) 

6.   Class  V.    Arachnida 

The  class  Arachnida  (Gr.  arachne,  a  spider)  includes  the 
spiders,  ticks,  mites,  scorpions,  and  king-crabs.  These  animals 
differ  markedly  from  one  another,  but  agree  in  several  important 
respects:  (i)  they  have  no  antennae;  (2)  there  are  no  true  jaws; 
(3)  the  first  pair  of  appendages  are  nippers,  termed  chelicerae; 
and  (4)  the  body  can  usually  be  divided  into  an  anterior  part, 
the  cephalo thorax,  and  a  posterior  part,  the  abdomen.  Twelve 
orders  of  arachnids  are  recognized  in  this  book.  The  first  four 
orders  Araneida,  Scorpionidea,  Phalangidea,  and  Acarina 
contain  most  of  the  living  species;  the  last  order,  Euryptertda, 
is  known  only  from  fossils. 

a.  The  Spiders 

Order  i .  Araneida.  —  Spiders.  —  Since  the  spiders  are  the 
most  common  of  all  arachAids,  they  are  used  here  to  illustrate 
the  anatomical  and  physiological  characteristics  of  the  class. 

External  Features.  —  Figure  313  shows  the  principal  external 
features  of  a  spider.  The  body  consists  of  a  cephalothorax  which 
is  undivided,  and  an  abdomen  which  is  usually  soft,  roimded,  and 
unsegmented. 


372 


COLLEGE  ZOOLOGY 


There  are  six  pairs  of  appendages  attached  to  the  cephalo- 
thorax.  Antennae  are  absent;  their  sensory  functions  are  in  part 
performed  by  the  walking  legs.  The  first  pair  of  appendages  are 
called  chelicerce  (Fig,  314,  ig).  They  are  in  many  species  com- 
posed of  two  parts,  a  basal  "mandible"  (Fig.  313,  B),  and  a 
terminal  claw.  Poison-glands  (Fig.  314,  20)  are  situated  in  the 
chelicerae.     The  poison  they  secrete  passes  through  a  duct  and 

out  of  the  end  of  the  chelicera 
(Fig.  314,  ig)\  it  is  strong 
enough  to  kill  insects  and  to 
injure  larger  animals.  The 
second  pair  of  appendages  are 
the  pedipalpi  (Fig.  313,  palpus 
and  maxilla)  ;  their  bases, 
called  "  maxillae,"  are  used  as 
jaws  to  press  or  chew  the 
food.  The  pedipalpi  of  the 
male  are  used  as  copulatory 
organs. 

Following  the  pedipalpi  are 
four  pairs  of  walking  legs.  This 
number      easily     distinguishes 


Fig.  313 

spider. 


External  features  of  a 


A,  under  surface;  all  but  one    spiders  from  insects,  since  tl\e 

leg  removed.     B,  front  of  head  show-     ^^^^^^  gg  ^^^      ^^ire^        :^^^ 

ing     eyes     and     mandibles.        (From  '-  ^  •'  ^ 

Emerton.)  Each    leg    consists    of    seven 

joints,  —  (i)  coxa,  (2)  tro- 
chanter, (3)  femur,  (4)  patella,  (5)  tibia,  (6)  metatarsus, 
(7)  tarsus,  —  and  is  terminated  by  two  toothed  claws  (Fig.  315) 
and  often  a  pad  of  hairs  {s)  which  enables  the  spider  to  run 
on  ceilings  and  walls.  The  bases  of  certain  of  the  legs  some- 
times serve  as  jaws. 

The  sternum  lies  between  the  legs,  and  a  "  labium  "  is  situated 
between  the  "  maxillae."  The  eyes,  usually  eight  in  number, 
are  on  the  front  of  the  head  (Fig.  313,  B).  The  mouth  (Fig.  314, 
i)  is  a  minute  opening  between  the  bases  of  the  pedipalpi  (max- 


PHYLUM   ARTHROPODA 


373 


illae);   it  serves  for  the  ingestion  of  juices  only,  since  spiders  do 
not  eat  solid  food. 

The  abdomen  is  connected  by  a  slender  waist  with  the  cephalo- 
thorax.     Near  the  anterior  end  of  the  abdomen  on  the  ventral 

22 

n 

24- 


13    15    14     13 

Fig.  314.  —  Diagram  of  a  spider,  Epeira  diademata,  showing  the  arrange- 
ment of  the  internal  organs.  /,  mouth;  2,  sucking  stomach;  3,  ducts  of  liver; 
4,  so-called  malpighian  tubules;  5,  stercoral  pocket;  6,  anus;  7,  dorsal  muscle 
of  sucking  stomach;  8,  caecal  prolongation  of  stomach;  g,  cerebral  ganglion 
giving  off  nerves  to  eyes;  10,  suboesophageal  ganglionic  mass;  //,  heart  with 
three  lateral  openings  or  ostia;  12,  lung  sac;  13,  ovary;  14,  acinate  and  pyri- 
form  silk  glands;  15,  tubuliform  silk  glands;  16,  ampuUiform  silk  gland; 
//,  dendriform  silk  glands;  18,  spinnerets;  ig,  distal  joint  of  chelicera;  20,  poison 
gland;  21,  eye;  22,  pericardium;  23,  vessel  bringing  blood  from  lung  sac  to 
pericardium;    24,  artery.     (From  the  Cambridge  Natural  History.) 

surface  is  the  genital  opening,  protected  by  a  pair  of  appendages 
which  have  fused  together  to  form  a  plate  called  the  epigynum 
(Fig.  313).  On  either  side  of  the  epigy- 
num is  the  slit-like  opening  of  the  respir- 
atory organs  or  lung  books  (Fig.  313; 
Fig.  314,  12).  Some  spiders  also  possess 
trachece  which  open  to  the  outside  near 
the  posterior  end  on  the  ventral  surface 
(Fig.  313).  Just  back  of  the  tracheal 
opening  are  three  pairs  of  tubercles  or 
spinnerets  (Fig.  313;  Fig.  314,  18),  used 
for  spinning  threads.  The  anus  (Fig. 
314,  6)  lies  posterior  to  the  spinnerets. 


Fig.  315.  —  End  of  foot 
of  a  spider,  Philceus  chrys- 
ops,  showing  two  claws 
and  pencil  consisting  of 
spatulate  hairs  (s).  (From 
Sedgwick's  Zoology,  after 
Hermann.) 


374  c(3llege  zoology 

Internal  Anatomy  and  Physiology  (Fig.  314). — The  food  of 
the  spider  consists  of  juices  sucked  from  the  bodies  of  other  ani- 
mals, principally  insects.  Suction  is  produced  by  the  enlarge- 
ment of  the  sucking  stomach  (Fig.  314,  2),  due  to  the  contraction 
of  muscles  attached  to  its  dorsal  surface  and  to  the  chitinous 
covering  of  the  cephalo thorax  (7).  The  true  stomach,  which 
follows  the  sucking  stomach,  gives  off  five  pairs  of  cceca  or  blind 
tubes  (8)  in  the  cephalothorax.  The  intestine  passes  almost 
straight  through  the  abdomen ;  it  is  enlarged  at  a  point  ( j)  where 
ducts  bring  into  it  a  digestive  fluid  from  the  "  liver, '^  and  again 
near  the  posterior  end,  where  it  forms  a  sac,  the  *'  stercoral  pocket " 
(5).  Tubes,  called  Malpighian  tubes  (4),  enter  the  intestine  near 
the  posterior  end.  The  alimentary  canal  is  surrounded  in  the 
abdomen  by  a  large  digestive  gland  or  "  liver."  This  gland  se- 
cretes a  fluid  resembling  pancreatic  juice  and  pours  it  into  the 
intestine  through  ducts  (j). 

The  circulatory  system  consists  of  a  heart,  arteries,  veins,  and 
a  number  of  spaces  or  sinuses.  The  heart  (Fig.  314,  //)  is  situ- 
ated in  the  abdomen  and  is  surrounded  by  the  digestive  glands. 
It  is  a  muscular,  contractile  tube  lying  in  a  sheath,  the  peri- 
cardium {22),  into  which  it  opens  by  three  pairs  of  ostia.  It 
gives  off  posteriorly  a  caudal  artery,  anteriorly  an  aorta  which 
branches  and  supplies  the  tissues  in  the  cephalothorax,  and  three 
pairs  of  abdominal  arteries  (24).  The  blood,  which  is  colorless 
and  contains  mostly  ameboid  corpuscles,  passes  from  the  ar- 
teries into  sinuses  aind  is  carried  to  the  book  lungs  {12)  where  it 
is  aerated;  it  then  passes  to  the  pericardium  by  way  of  the 
pulmonary  veins  {2J),  and  finally  enters  the  heart  through  the 
ostia. 

Respiration  is  carried  on  by  tracheae  and  book  lungs ;  the  latter 
are  peculiar  to  arachnids.  The  book  lungs  (Fig.  314,  12),  of 
which  there  are  usually  two,  are  sacs,  each  containing  generally 
from  fifteen  to  twenty  leaf-like  horizontal  shelves  through  which 
the  blood  circulates.  Air  entering  through  the  external  openings 
is  thus  brought  into  close  relationship  with  the  blood.     Tracheae 


PHYLUM   ARTHROPOD  A  375 

are  also  usually  present,  but  do  not  ramify  to  all  parts  of  the  body 
as  in  the  insects  (p.  320,  Fig.  242). 

The  excretory  organs  are  the  Malpighian  tubules  (Fig.  314,  4), 
which  open  into  the  intestine,  and  two  coxal  glands  in  the  cepha- 
lothorax.     The  coxal  glands  are  sometimes  degenerate,  and  their 


Fig.  316.  — Orb  web  of  a  spider,  Epeira.     a,  first  spiral  line;  b,  second 
spiral  line;  c,  line  to  nest.     (From  Davenport,  after  Emerton.) 

openings  are  difficult  to  find;  they  are  homologous  with  the  green 
glands  of  the  crayfish  (p.  284,  Fig.  202,  40-42). 

The  nervous  sy stein  consists  of  a  bilobed  ganglion  above  the 
oesophagus  (Fig.  314,  g),  a  suboesophageal  ganglionic  mass  (lo), 
and  the  nerv^es  which  arise  from  them.  There  are  sensory  hairs 
on  the  pedipalps  and  probably  on  the  walking  legs,  but  the  prin- 
cipal sense-organs  are  the  eyes.  There  are  usually  eight  eyes 
(Fig.  313,  B;   Fig.  314,  21),  and  these  differ  in  size  and  arrange- 


376 


COLLEGE  ZOOLOGY 


ment  in  different  species.     Spiders  apparently  can  see  objects 
distinctly  only  at  a  distance  of  four  or  five  inches. 

The  sexes  are  separate,  and  the  testes  or  ovaries  (Fig.  314,  ij) 
form  a  network  of  tubes  in  the  abdomen.    The  spermatozoa  are 


Fig.  317. — A,  crab-spider,  Thomisus.  B,  jumping-spider,  Attus.  C,  young 
spider,  Lycosa,  preparing  for  an  aerial  voyage.  D,  house-spider,  Theridium 
epidariorum.     (A,  B,  C,  from  Davenport,  after  Emerton ;    D,  from  Emerton.) 


transferred  by  the  pedipalps  of  the  male  to  the  female,  and  fer- 
tilize the  eggs  within  her  body.  The  eggs  are  laid  in  a  silk  co- 
coon, which  is  attached  to  the  web  or  to  a  plant,  or  carried  about 
by  the  female.  The  young  leave  the  cocoon  as  soon  after  hatch- 
ing as  they  can  run  about. 

The  spinning  organs  of  spiders  are  three  pairs  of  appendages 
called  spinnerets  (Fig.  313;  Fig.  314,  18).  The  spinnerets  are 
pierced  by  hundreds  of  microscopic  tubes  through  which  a  fluid 


PHYLUM  ARTHROPOD  A  377 

secreted  by  a  number  of  abdominal  silk  glands  (Fig.  314,  14-if)^ 
passes  to  the  outside  and  hardens  in  the  air,  forming  a  thread. 
These  threads  are  used  to  build  nests,  form  cocoons,  spin  webs, 
and  for  many  other  purposes.  An  orh  web,  such  as  is  shown  in 
Figure  3 16,  is  spun  in  the  following  manner.  A  thread  is  stretched 
across  the  space  selected  for  the  web;  then  from  a  point  on  this 
thread  other  threads  are  drawn  out  and  attached  in  radiating 
lines.  These  threads  all  become  dry  and  smooth.  On  this 
foundation  a  spiral  is  spun  of  sticky  thread.  The  spider  stands 
in  the  center  of  the  web  or  retires  to  a  nest  at  one  side  and  waits 
for  an  insect  to  become  entangled  in  the  sticky  thread;  it  then 
rushes  out  and  spins  threads  about  its  prey  until  all  struggles 
cease. 

Many  spiders  do  not  spin  webs,  but  wander  about  capturing 
insects,  or  lie  in  wait  for  them  in  some  place  of  concealment.  In 
this  group  belong  the  crab-spiders  (Thomisid^,  Fig.  317,  A), 
jumping-spiders  (Attid^e,  Fig.  317,  B),  ground-spiders  (Dras- 
siD^),  and  running  spiders  (Lycosid^,  Fig.  317,  C).  The  cob- 
web spiders  spin  various  kinds  of  nets  for  capturing  insects.  The 
tube-weavers  (Agelenid^)  build  platforms  on  the  grass  and 
hide  in  a  tube  at  one  side;  the  line  weavers  (LiNYPHiADiE)  spin 
flat  webs  with  irregular  meshes;  the  round-web  spiders  (Epeiri- 
d^e)  build  webs  like  that  shown  in  Figure  316;  and  theTHERi- 
DiD^  (Fig.  317,  D)  build  irregular  webs  in  comers  and  on  plants. 

b.  Other  Arachnida 

Order  2.  Scorpionidea.  —  Scorpions.  —  The  scorpions  are 
rapacious  arachnids  measuring  from  half  an  inch  to  eight  inches 
in  length.  They  live  in  tropical  and  subtropical  regions,  hiding 
in  crevices  or  in  pits  in  the  sand  during  the  daytime,  but  nmning 
about  actively  at  night.  They  capture  insects  and  spiders  with 
their  pedipalpi  (Fig.  318),  tear  them  apart  with  their  chelicerae, 
and  devour  the  pieces.  Larger  animals  are  paralyzed  by  the 
sting  on  the  end  of  the  tail.  This  sting  does  not  serve  as  a  weapon 
of  defense  unless  the  scorpion  is  hard  pressed;  and  is  not  used,  as 


378 


COLLEGE  ZOOLOGY 


is  often  stated,  to  sting  itself  to  death,  since  its  poison  has  no 
effect  upon  its  own  body. 

The  scorpion's  body  (Fig.  318)  is  more  obviously  segmented 
than  that  of  most  of  the  other  arachnids.  There  is  a  cephalo- 
thorax  (prosoma),  and  an  abdomen  of  two  parts  —  a  thick  an- 
terior portion  (mesosoma),  and  a  slender  tail  (metasoma)  which 


,Pe<iipalp 
Lateral  eyes 
'\Miet£tan  eyes 


Fig.  318.  —  Scorpion,  Buthus  occiianus.     A,  dorsal  view.     B,  ventral  view. 
(From  the  Cambridge  Natural  History,  after  Kraepelin.) 

is  held  over  the  back  when  the  animal  walks.  The  dorsal  shield 
of  the  cephalothorax  bears  a  pair  of  median  eyes  and  three  lateral 
eyes  on  each  side.  The  sense  of  sight  is,  however,  poorly  de- 
veloped. On  the  ventral  surface  of  the  second  abdominal  seg- 
ment are  two  comb-like  appendages  called  pectines  (Fig.  318,  B) ; 
these  are  probably  special  tactile  organs.     Tactile  hairs  are  dis- 


PHYLUM  ARTHROPODA 


379 


tributed  over  the  body,  and  the  sense  of  touch  is  quite  delicate. 
There  are  four  pairs  of  lung  books  opening  by  means  of  stigmata 
(Fig.  318,  B)  on  the 
under  surface  of  ab- 
dominal segments 
III-VI. 

The  mating  activi- 
ties of  scorpions  are 
very  curious,  and 
include  a  sort  of 
promenade     (Fig. 

319)- 

viviparous.        The 

young  ride  about  upon  the  back  of  the  female  for  about  a  week, 

and  then  shift  for  themselves.     They  reach  maturity  in  about 

five  years. 

Order    3.    Phalangidea.  —  Harvestmen    or    Daddy-long- 
legs. —  The  harvestmen  may  be  distinguished  from  spiders  by 


Fig.  319. — The    "promenade   a   (fewx "   of    the 
Scoroions  are    ^'^^''P^®^'  Buthus  occUanus.     (From  the  Cambridge 
^  Natural  History,  after  Fabre.) 


Fig.  320. 


Order  Phalangidea.     Harvestman,  Phalangium  opilio,  male. 
(From  Sedgwick's  Zoology.) 


their  extremely  long  legs  (Fig.  320),  the  absence  of  a  waist,  and 
their  segmented  abdomen.  They  are  able  to  run  rapidly  over 
leaves  and  grass.     Their  food  consists  of  small  living  insects. 

Order  4.  Acarina.  —  Mites  and  Ticks.  —  These  are  minute 
arachnids  without  any  external  signs  of  segmentation.  Many  of 
them  are  parasitic  and  often  cause  serious  diseases. 


3^0 


COLLEGE  ZOOLOGY 


The  family  Trombidiid^  includes  the  harvest  mites  or 
*' chiggers  "  (Fig.  321).  These  little  creatures  are  transferred 
by  contact  from  plants  to  the  bodies  of  man  and  other  animals. 

They  burrow  into  the  skin, 
with  painful  results. 
Treatment  with  a  one  or 
two  per  cent  solution  of 
carbolic  acid  is  the  proper 
remedy.  The  poultry 
tick,  Dermanyssus  gallincB 
(Fig.  322,  A)  belongs  to 
the  family  GAMASiDiE.  It 
sucks  the  blood  of  chickens, 
and  is  a  pest  on  poultry 
farms. 
The  family  Ixodid.'E  contains  a  number  of  injurious  species. 
The  cattle  tick,  Boophilus  {Mar gar  opus)  annul  atus  (Fig.  322,  B), 
is  perhaps  the  most  important.  These  ticks  cling  to  the  skin  of 
cattle  with  their  strong  mouth-parts,  and  suck  the  blood  of  their 
host.  When  full  grown  the  females  drop  to  the  ground  and  lay 
from  2000  to  4000  eggs;  these  soon  hatch,  and  the  young  crawl 
upon  a  blade  of  grass  and  wait  for  cattle  to  come  past  to  which 
they  can  fasten  themselves.     The  principal  injury  done  by  the 


Fig.  321.  —  Order  Acarina.  Harvest- 
mites  or  "  chiggers."  Leptus  irritans  on 
the  right;  L.  americana  on  the  left.  (From 
Osborn,  after  Riley.) 


Fig.  322. 


Order  Acarina.     A,  poultry  tick,  Dermanyssus  gallince,  young. 
B,  cattle  tick,  Boophilus  annulatus. 


PHYLUM  ARTHROPODA 


381 


Fig.  322,  continued.  —  Order  Acarina.  C,  follicle  mite,  Demodex  folliculorum. 
D,  itch-mite,  Sarcoptes  scabiei.  E,  sheep-scab  mite,  Psoroptes  communis  var. 
ovis  (A,  B,  E,  from  Osborn  ;  B,  after  Packard;  C,  D,  from  Sedgwick's  Zoology  ; 
C,  after  Megnin,  D,  after  Gudden.) 


ticks  is  the  transference  of  a  sporozoan  parasite,  Piroplasma 
bigeminum,  from  the  blood  of  one  animal  to  that  of  another. 
This  parasite  produces  Texas  fever,  a  disease  that  causes  an 
annual  loss  of  about  $100,000,000  in  the  United  States. 

Other  members  of  the  order  Acarina  that  should  be  men- 
tioned are:  (i)  the  follicle  mites,  Demodex  folliculorum  (Fig.  322, 
C),  that  lives  in  the  sweat-glands  and  hair  follicles  of  man  and 
some  domestic  animals,  causing  what  are  known  as  ''black- 
heads "  ;  (2)  the  itch-mite, 
Sarcoptes  scabiei  (Fig.  322,  D) 
which  burrows  beneath  the 
epidermis  of  man  and  causes 
intense  itching;  and  (3)  the 
scab  parasite,  Psoroptes  com- 
munis (Fig.  322,  E),  which 
feeds  on  the  skin  of  sheep, 
cattle,  and  horses,  producing 
scabs.  Fig.    323.  — Order   Pedipalpi.      A 

order    S-      Pedipalpi    (Fig.     ^.^^'^^Z^rS^t^l   k'ZT 

323). — The    members    of    this      palpi.     (From  Sedgwick's  Zoology.) 


382 


COLLEGE  ZOOLOGY 


order  have  large,  conspicuous  pedipalps  (Kt).  They. are 
nocturnal  in  habit  and  live  under  stones  and  in  crevices  during 
the  day.  They  inhabit  the  warm  countries  and  feed  chiefly  on 
insects. 

Order  6.     Palpigradi  (Fig.  324).  —  One  family  and  two  genera 
belong  to  this  order.     They  are  small  (about  i  mm.  long)  and 


Fig.  324.  Fig.  32*5.  Fig.  326. 

Fig.  324.  —  Order  Palpigradi.  Kaenenia  mirabilis.  (From  the  Cam- 
bridge Natural  History,  after  Hansen.) 

Fig.  325.  —  Order  SoLiFUGiE.  Rhagodes,  ventral  view,  a,  anus;  ch,  cheli- 
cerae;  g.o,  genital  operculum;  n,  racket  organs;  p,  pedipalp;"  /,  2,  3,  4,  walking 
legs.     (From  the  Cambridge  Natural  History,  after  Bernard.) 

Fig.  326.  —  Order  Chernetidia.  Obisium  trombidioides.  Kt,  pedipalp. 
(From  Sedgwick's  Zoology.) 

widely  distributed.  Several  species  have  been  recorded  from 
Texas. 

Order  7.  Solifugae. — The  Solifug^  .  (Fig.  325)  are  fair 
sized,  hairy  arachnids  living  in  warm  parts  of  the  globe.  About 
one  hundred  and  seventy  species  are  known. 

Order  8.  Chernetidia  (Pseudoscorpionida,  Fig.  326.)  — 
These  are  brownish  arachnids  from  one  eighth  to  one  fourth  of 
an  inch  in  length.  They  possess  comparatively  large  pedipalps 
with  which  they  capture  their  insect  food.  Large  insects  to 
which  they  cling  often  carry  them  about  —  a  fact  that  probably 
accounts  for  their  wide  distribution.     There  is  only  one  family. 


PHYLUM  ARTHROPODA 


383 


Order  9.  Xiphosura.  —  King-Crabs.  —  The  king-crab  or 
horseshoe  crab,  Limulus  polyphemus  (Fig.  327),  occurs  along  the 
Atlantic  coast  from  Maine  to  Yucatan.  It  differs  from  other 
arachnids  in  the  presence  of  gills  (Fig.  327,  B,  11-15)  and  the 
absence  of  Malpighian  tubules.  The  king-crabs  and  a  few  mites 
are  the  only  li\'ing  marine  arachnids.     Limulus  is  a  burrowing 


Fig.  327.  —  Order  Xiphosura.  King-crab,  Limulus  polyphemus.  A,  dorsal 
view.  I,  carapace ;  2,  meso-  and  meta-soma ;  3,  telson ;  4,  median  eye ; 
5,  lateral  eye.  B,  ventral  view.  /,  carapace ;  2,  meso-  and  meta-soma ; 
3,  telson;  4,  chelicera;  5,  pedipalp;  6,  7,  S,  9,  3d  to  6th  appendages,  walking 
legs;  10,  genital  operculum  turned  forward  to  show  genital  aperture;  //,  12, 
13,  14,  15,  appendages  bearing  gill  books;  16,  anus;  17,  mouth;.  18,  chilaria. 
(From  Shipley  and  MacBride.) 


animal  and  lives  in  the  sand.  It  may  be  active  at  night,  mo\ing 
by  ''  short  swimming  hops,  the  respiratory  appendages  giving 
the  necessary  impetus,  whilst  between  each  two  short  flights  the 
animal  balances  itself  for  a  moment  on  the  tip  of  its  tail."  The 
food  of  Limulus  consists  chiefly  of  worms,  such  as  Nereis  (Fig. 
163),  and  mollusks.  These  are  caught  while  burrowing  through 
the  sand,  are  held  by  the  chelicerae,  and  chewed  by  the  bases  of 
the  walking  legs.  In  the  spring  the  king-crabs  come  near  shore 
to  spawn. 


384 


COLLEGE  ZOOLOGY 


Order  lo.  Eurypterida  (Fig.  328).  —  The  Eurypterida 
lived  in  both  salt  water  and  fresh  water  during  the  Silurian  and 
Devonian  periods  (Table  XVII),  and  are  known  to  us  only  as 
fossils.  They  appear  to  represent  a  condition  intermediate  be- 
tween Limulus  and  the  Scorpionidea. 


Fig.  328.  Fig.  330.  Fig.  331. 

Fig.  328.  —  Order  Eurypterida.  Eurypterus  fischeri,  dorsal  surface. 
a,  ocellus;  b,  lateral  eye;  2-6,  appendages  of  prosoma;  7-12,  segments  of 
mesosoma;  13-18,  segments  of  metasoma;  iq,  tail  spine.  (From  the  Cam- 
bridge Natural  History,  after  Holm.) 

Fig.  329.  —  Pycnogonida.  Ammothea  pycnogonoides.  (From  Sedgwick's 
Zoology,   after  regne   animal.) 

Fig.  330. — Tardigrada.  Macrobiotus  schuUzei.  3/ J,  stomach;  O,  mouth; 
OzJ,  ovary;  5/»i,  salivary  glands;  T,  malpighian  tubules;  Fw,  pharynx ;  Vs, 
accessory  gland.     (From  Sedgwick's  Zoology,  after  GreeflF.) 

Fig.  331.  —  Pentastomida.  Pentastomum  tcenioides.  A,  anus;  D,  intes- 
tine;   HJ,  hooks;    0,  mouth.     (From  Sedgwick's  Zoology.) 


PHYLUM  ARTHROPODA  385 

It  is  convenient  to  mention  at  this  point  three  groups  of  pe- 
culiar animals  that  are  often  placed  in  the  class  Arachnida: 
(i)  the  Pycnogonida  (Pantopoda),  (2)  the  Tardigrada,  and 
(3)  the  Pentastomida.  The  Pycnogonida  (Fig.  329)  are  marine 
animals  with  small  bodies  and  long  legs.  They  crawl  about  over 
seaweeds  and  coelenterates,  th©  juices  of  which  they  suck.  The 
Tardigrada,  or  "  bear-animalcules "  (Fig.  330),  are  minute 
creatures  from  0.3  mm.  to  i  mm.  in  length.  They  live  on  tree 
trunks,  and  in  the  debris  in  ditches.  The  Pentastomida  (Fig. 
331)  are  parasitic  in  the  noses  of  flesh-eating  vertebrates. 


CHAPTER    XIV 

PHYLUM    CHORDATA:    INTRODUCTION 

The  Phylum  Chordata  (Lat.  chordatus,  having  a  cord)  in- 
cludes the  vertebrate  animals  (mammals,  birds,  reptiles,  am- 
phibians, fishes,  elasmobranchs,  and  cyclostomes)  and  a  number 
of  marine  forms  (Figs.  332  to  341)  that  are  not  generally  known 
except  to  zoologists.  All  of  these  animals  are  characterized  at 
some  stage  in  their  existence  by  (i)  a  skeletal  axis,  the  nntnr.hnrd^ 

(2)  by  Mired  slits  connecting  the  pharynx  with  the  exterior,  and 

(3)  by  a  central  nerve-cord  dorsal  to  the  alimentary  canal  and  con- 
taining a  cavity  or  system  of  cavities,  the  neurocoele.  In  many 
respects  the  chordates  differ  widely  from  one  another,  and  it  is 
customary  to  separate  them  into  four  subphyla :  — 

(i)  The  Enteropneusta  (Gr.  enteron,  intestine;  pneuma, 
breathe),  containing  two  orders  of  worm-like  animals  of  some- 
what doubtful  systematic  position, 

(2)  The  TuNiCATA  (Lat.  tunica,  mantle),  or  sea-squirts,  and  a 
number  of  other  marine  forms, 

(3)  The  Cephalochorda  (Gr.  kephale,  head;  chorde,  cord), 
comprising  only  two  families  of  fish-like  animals  called  lancelets, 
and 

(4)  The  Vertebrata  (Lat.  vertebratus,  jointed). 

I.  SuBPHYLUM  I.    Enteropneusta 

This  subphylum  is  sometimes  given  the  names  Hemichorda 
or  Adelo CHORDA.  It  contains  two  orders:  (i)  the  Balano- 
GLOSSIDA,  and  (2)  the  Cephalodiscida.  Four  families  and 
about  ten  genera  are  recognized  in  the  order  Balanoglossida, 

386 


PHYLUM   CHORDATA 


387 


but  only  two  genera,  Cephalodiscus  (Fig.  336) 
and  Rhabdopleura  (Fig.  335),  belong  to  the  order 
Cephalodiscida. 

The  external  features  of  one  of  the  Balano- 
GLOSSiDA  are  shown  in  Figure  332.  Three 
regions  may  be  distinguished:  a  proboscis  (/), 
a  collar  (2),  and  a  trunk  (jf.  Paired  lateral 
gill-slits  (5)  are  present  in 
the  anterior  part  of  the 
trunk.  The  mouth  opens 
on  the  anterior  surface  of 
the  collar  region  {4),  and 
the  anus  is  situated  at  the 
posterior  end  of  the  trunk. 
The  proboscis  and  collar  pos- 
sess cavities  which  become 
filled  with  water  through 
ciliated  pores  (Fig.  ^:^^,  8). 
When  in  a  swollen  condition,  the  proboscis  and  collar  are  forced 
into  the  sand  or  mud,  and  constitute  effective  burrowing 
instruments. 

Figure   333   shows   diagrammatically   the  principal   internal 
structures  of  Glossobalanus.     The  notochord  {11)  is  a  supporting 


Fig.  332. — Dolichoglossus  kowalevskii. 
/.proboscis;  2,  collar;  j,  trunk;  4,  mouth; 
5,  gill-slits.  (From  Shipley  and  Mac- 
Bride,  after  Spengel.) 


Fig.  333.  -T  Lonojitudinal  section  through  the  middle  line  of  Glossobalanus. 
I,  proboscis;  2,  collar;  3,  trunk;  '4,  proboscis  cavity;  5,  glomerulus;  6,  peri- 
cardium; 7,  heart;  8,  proboscis  pore;  9,  collar  cavity;  10,  mouth;  //,  noto- 
chord; 12,  dorsal  blood-vessel;  13,  oesophagus;  14,  branchial  region  of  ali- 
mentary canal;  15,  ventral  blood-vessel;  16,  gill-slits;  77,  central  nervous 
system;  18,  dorsal  roots  of  nervous  system;  iq,  ventral  pocket  of  proboscis 
cavity.     (From  Shipley  and  MacBride.) 


388. 


COLLEGE  ZOOLOGY 


organ  consisting  of  a  hollow  tube  of  cells;  it  opens  posteriorly 
into  the  alimentary  canal.  The  alimentary  canal  is  straight. 
Mud  in  which  the  animals  live  is  taken  into  the  mouth  {id)  and 
forced  slowly  through  the  digestive  tube,  where  nutriment  is  ex- 
tracted from  the  organic  matter  contained  in  it  —  a  process 
similar  to  digestion  in  the  earthworm  (p.  219).  The  gill-slits 
or  branchial  clefts  {16)  open  into  the  anterior  portion  of  the  ali- 
mentary canal  and  supply  water  to  the 
tongue-like  respiratory  organs. 

There  is  a  dorsal  blood-vessel  {12)  ending 
anteriorly  in  a  contractile  heart  (7)  which 
lies  in  a  pericardial  cavity  (6).  A  ventral 
blood-vessel  (75)  is  connected  with  the 
dorsal  blood-vessel  in  the  collar  region  by 
two  lateral  tubes.  The  other  blood- 
vessels are  simply  spaces  in  the  tissues. 
Excretory  products  appear  to  be  ex- 
tracted from  the  blood  by  the  glomerulus 
Tornaria  or  kidney  (5),  which  lies  on  the  posterior 
wall  of  a  cavity  in  the  proboscis  (4).  The 
excretions  pass  out  through  the  proboscis 
pore  {8)  when  water  is  expelled  from  the 
proboscis  cavity. 

The  nervous  system  is  not  concentrated. 
A  layer  of  nerve- fibers  just  beneath  the  ectoderm  makes  the 
entire  surface  sensitive.  Thickenings  occur  along  the  mid-dorsal 
and  mid-ventral  lines  of  the  trunk  and  around  the  trunk  just 
posterior  to  the  collar.  A  neural  tube  {if)  is  formed  by  the  dorsal 
thickening.  The  ccelom  which  arises  from  the  primitive  digestive 
tract,  very  much  as  in  echinoderms  (p.  210,  Fig.  150,  A,  cm),  is 
represented  by  a  proboscis  cavity  (Fig.  2>?>?>y  4)^  two  collar 
cavities  (p),  and  two  trunk  cavities. 

The  sexes  are  separate.  The  ovaries  or  testes  form  a  double 
row  in  the  anterior  trunk  region,  and  the  germ-cells  reach  the 
exterior  through  pores  in  the  body-wall.     In  some  species  each 


334 


larva  of  Enteropneusta. 
A,  anus;  O,  mouth; 
S,  apical  plate;  W,  rudi- 
ment of  proboscis  ccelom. 
(From  Sedgwick's  Zool- 
ogy,  after   Metchnikofif.) 


PHYLUM   CHORDATA 


389 


egg  develops  into  a  free-swimming  larva  called  a  Tornaria  (Fig. 
334).  When  first  discovered,  these  larvae  were  thought  to  belong 
to  an  echinoderm.  The  resemblance  of  the  Tornaria  to  the  larvae 
of  echinoderms  (Figs.  1 50-1 51)  is  quite  striking  and  has  led  to 


^^'^^ 


Fig.  335.  —  Rhabdo  pleura, 
a,  mouth;  b,  anus;  c,  stalk; 
d,  proboscis;  e,  intestine;  /,  an- 
terior region  of  trunk;  g,  a  ten- 
tacle. (From  Parker  and  Has- 
well,  after  Lankester.) 


Fig.  336.  —  Cephalodiscus  dodeca- 
lophus,  anterior  view.  /,  tentacles; 
2,  proboscis  (buccal  shield);  3,  pig- 
ment band  on  proboscis ;  4,  buds ; 
5,  pedicle;  6,  trunk.  (From  Sedg- 
wick's Zoology,  after  Mcintosh.) 


a  rather  plausible  theory  of  the  origin  of  the  vertebrates  (Chap. 
XXII). 

Rhabdopleura  (Fig.  335)  and  Cephalodiscus  (Fig.  336)  are 
colonial  Enteropneusta  inhabiting  the  deep  sea.  They  have 
the  power  of  reproducing  by  means  of  buds  (Fig.  336,  4). 
Cephalodiscus  has  only  one  pair  of  gill-slits;    Rhabdopleura  has 


none. 


2.     SUBPHYLUM   II.      TUNICATA 


The  TuNiCATA  or  IJrochorda  (Fig.  337)  all  live  in  the  sea. 
They  are  either  free-swimming  or  attached,  are  widely  distrib- 
uted, and  occur  at  all  levels  from  near  the  surface  to  a  depth  of 


390 


COLLEGE  ZOOLOGY 


over  three  miles.  They  range  in  size  from  about  a  hundredth 
of  an  inch  to  over  a  foot  in  diameter.  Some  are  brilliantly 
colored.  The  adult  (Fig.  338)  is  often  sac-like  and  has  received 
the  common  name  "  sea-squirt  "  because  when  irritated  it  may 
eject  water  through  two  openings  in  the  unattached  end  (Fig. 
338,  I,  2).     The  term  tunicata  is  applied  to  members  of  the 

group  on  account 
of  a  cuticular  outer 
covering  known  as 
a  test  or  tunic. 

The  chordate 
characteristics  of 
tunicates  were  not 


recognized  until  the 
development  of  the 
egg  and  metamor- 
phosis of  the  larva 
were  fully  investi- 
gated (Kowalevsky, 
1866).  It  was  then 
discovered  that  the 
t)^ical  larva  (Fig. 
339) ,  which  is  about 
a  quarter  of  an  inch 
long  and  resembles 
a  frog  tadpole,  pos- 
sesses (i)  a  distinct 
notochord  (A,  noto)^ 
(2)  a  neural  tube  in  the  tail  which  enlarges  in  the  trunk 
(A,  med),  ends,  in  a  vesicle  (A,  sens.ves),  and  is  considered 
the  forerunner  of  the  brain  of  the  Vertebrata,  and  (3)  a 
pharynx  which  opens  to  the  exterior  by  ciliated  gill-slits 
(A,  stig).  The  tail  propels  the  larva  forward  by  lateral  strokes. 
After  a  short  existence  as  a  free-swimming  organism  the  larva 
becomes  attached  to  some  object  by  three  projections  on  the 


Fig.  337.  —  Sketch  of  the  chief  kinds  of  Tunicata 
found  in  the  sea.  (From  the.  Cambridge  Natural 
History.) 


PHYLUM  CHORDATA 


391 


anterior  end  (Fig.  339,  A,  adh)  which  secrete  a  sticky  fluid 
It  then  undergoes  a  retrogressive  metamor-  t 

phosis  during  which  the  tail  with  the  noto- 
chord  and  neural  tube  disappear,  and  other 
changes  take  place  as  shown  in  Figure  339. 

The  typical  adult  tunicate  (Fig.  338)  is 
attached  by  a  stalk  {g)  and  surrounded  by  a 
tunic.  At  the  distal  end  are  two  openings; 
one  is  the  mouth  (i),  or  branchial  aperture, 
into  which  a  current  of  water  passes;  the 
other  (2)  is  the  atrial  orifice  through  which 
the  water  escapes  to  the  outside.  This 
current  of  water  brings  food  into  the  ali- 
mentary canal,  furnishes  oxygen  for  respira- 
tion, and  carries  away  excretory  substances. 
Near  the  mouth  is  a  ring  of  tentacles  {10) 
forming  a  sensory  sieve  through  which  in- 
coming water  and  food  must  pass.  Micro- 
scopic plants  and  animals  are  entangled  in 
mucus  secreted  by  a  pharyngeal  groove  or 
endostyle  (Fig.  339,  C,  end)  which  forms  a 
peripharyngeal  band  (Fig.  338,  11).  The 
alimentary  canal  is  bent  upon  itself  {6,  7), 
and  opens  into  the  atrial  cavity  (j).  A 
single  ganglion,  the  brain  (12),  lies  between 
the  branchial  and  atrial  tubes.  Tunicates 
are  hermaphroditic.  The  reproductive 
organs  lie  near  the  intestinal  loop  (8),  and 
their  ducts  open  (4)  near  the  anus.  Many 
species  reproduce  asexually  by  budding. 

There  are  three  orders  of  tunicates  (Fig. 
337):  (i)  the  AsciDiACEA,  (2)  the  Thaliacea, 
and  (3)  the  Larvacea. 

Order  i.  Ascidiacea  (Fig.  337,  lower 
portion). — The  tunicates  belonging  to  this 


Fig.  338.  — a  Tuni- 
cate, Ciona  intestinalis . 

I,  mouth;  2,  atrial  ori- 
fice; 3.  anus;  4,  geni- 
tal pore  ;  5,  muscles ; 
6,  stomach  ;  7,  intes- 
tine; 8,  reproductive 
organs;  q,  stalk; 
10,    tentacular    ring ; 

II,  peripharyngeal 
ring;  72,  brain.  (From 
Shipley  and  Mac- 
Bride.) 


392 


COLLEGE  ZOOLOGY 
A 


reel        '^r 

\    mea  j    9ens.r/&s 


ht 


sti^     ^'^     cuih 


Fig.  339.  —  Diagram  of  the  metamorphosis  of  the  free,  tailed  larva  inta 
the  fixed  Tunicate.  A,  stage  of  free-swimming  larva.  B,  recently  fixed  larva. 
C,  older  fixed  stage,  atr,  atrial  cavity;  cil.gr.  ciliated  groove  on  wall  of 
pharynx;  end,  endostyle;  ht,  heart  ;  med,  trunk -ganglion;  n.gn,  ganglion; 
nolo,  notochord ;  or,  branchial  aperture;  rect,  intestine;  sens.ves,  sensory 
vesicle ;  slig,  gill-slits ;  siol,  shoot  from  which  buds  rise ;  /,  cast  cellulose 
envelope  of  tail.     (From  Davenport,  after  Seeligft.) 


PHYLUM   CHORDATA 


393 


group  are  either  free-swimming  or  fixed,  colonial  or  solitary. 
The  colonial  forms  reproduce  asexually  by  budding,  as  well  as 
sexually.  Examples : 
Ciona  (Fig.  338),  Cyn- 
thia, Molgula,  Botryllus, 
Pyrosoma. 

Order  2.  Thaliacea 
(Fig.  337,  central  por- 
tion). —  These  are  free- 
swimming,  solitary,  or 
colonial  forms  living  near 
the  surface  of  the  sea, 
i.e.  pelagic.  The  com- 
monest genus,  Salpa 
(Fig.  340,  A),  is  cylin- 
drical, and  its  hoop-like 
muscle  bands  cause  it  to 
resemble  a  barrel.  Usu- 
ally there  is  an  alterna- 
tion of  generations  ;  a 
solitary  individual  gives 
rise  asexually  to  a  row  of 
sexual  members,  each  of 
which  produces  a  single  egg;  the  eggs  develop  into  asexual 
solitary  individuals. 

Order  3.  Larva'cea  (Fig.  337,  upper  portion). — The  Lar- 
VACEA  are  small  pelagic  forms  which  retain  the  larval  condition 
throughout  life.  Examples:  Appendicularia,  Oikopleura  (Fig. 
340,  B). 

3.  SUBPHYLUM  III.   CePHALOCORDA 

This  subphylum  contains  about  a  dozen  species  of  marine 
animals  of  which  Branchiostoma  lanceolatus,  commonly  known  as 
Amphioxus  or  the  Lancelet,  is  the  form  usually  studied.  Am- 
phioxus  is  of  special  interest,  since  it  exhibits  the  characteristics 


Fig.  340.  —  A,  a  solitary  Tunicate,  Salpa 
democratica,  dorsal  view.  /,  muscle  bands; 
2,  "  gill  "  ;  3,  endostyle;  4,  peripharyngeal 
band;  5,  brain;  d,  ciliated  pit;  ^."nucleus" 
of  stomach,  liver,  intestine;  q,  stolon;  10,  pro- 
cess of  mantle;  //,  mouth.  (From  Shipley 
and  MacBride,  after  Brooks.)  B,  Oikopleura 
cophocerca  in  its  test.  (From  Sedgwick's 
Zoology,  after  Fol.) 


394  COLLEGE  ZOOLOGY 

of  the  chordates  in  a  simple  condition.  Furthermore  it  is  prob- 
ably similar  to  the  ancestors  of  the  Vertebrata. 

Amphioxus  is  several  inches  long.  The  semi-transparent 
body  is  pointed  at  both  ends  and  laterally  compressed.  It  is 
found  near  the  shore,  where  it  burrows  in  the  clean  sand  with 
its  head  or  tail,  and  conceals  all  but  the  anterior  end.  It  some- 
times leaves  its  burrow  at  night  and  swims  about  by  means  of 
rapid  lateral  movements  of  the  body.  When  it  ceases  to  move, 
it  falls  on  its  side. 

External  Features  (Fig.  341).  —  Although  Amphioxus  is 
shaped  Hke  a  fish,  it  differs  from  the  latter  in  many  important 
respects  both  externally  and  internally.     There  are  no  lateral 


msz. 


ves. 


vel.  S'  /^    '^ 


Fig.  341.  —  An  adult  specimen  of  Branchiostoma  lanceolatus,  seen  from  the 
left  side  as  a  transparent  object,  an.,  anus ;  atp.,  atriopore  c,  caudal  fin ; 
ci.,  buccal  cirri;  df,  dorsal  fin;  e,  eye-spot;  fr,  fin-rays;  g^,  g^^,  twenty-six  pairs 
of  gonadial  pouches;  m^,  m^^,  m^^,  myotomes;  n,  neural  tube;  nch.,  notochord; 
vel.,  velum;   ves.,  vestibule;   vf.,  ventral  fin.     (From  Bourne.) 

fins  and  no  distinct  head.  Along  the  mid-dorsal  line  is  a  low 
dorsal  fin  (df)  extending  the  entire  length  of  the  body  and  widen- 
ing at  the  posterior  end  into  a  caudal  fin  (c).  The  caudal  fin 
extends  forward  on  the  ventral  surface  (vf.).  Both  dorsal  and 
ventral  fins  are  strengthened  by  rods  of  connective  tissue,  called 
fin-rays  (fr).  In  front  of  the  ventral  fin  the  lower  surface  of 
the  body  is  flattened,  and  on  each  side  is  an  expansion  of  the 
integument  called  the  metapleural  fold  (Fig.  342,  mp). 

The  body -wall  is  divided  into  a  number  (62)  of  V-shaped  muscle 
segments,  the  myotomes  (Fig.  341,  m^,  m^^,  m^^);  these  are  sepa- 
rated from  one  another  by  septa  of  connective  tissue.  The  myo- 
tomes on  one  side  of  the  body  alternate  with  those  on  the  other 
side.     The  muscle  fibers  contained  in  them  are  longitudinal,  and, 


PHYLUM   CHORDATA 


395 


since  they  are  attached  to  the  connective  tissue  partitions,  are  able 

to  produce  the  lateral  movements  of  the  body  used  in  swimming. 

The  mouth  opening  is  at  the  bottom  of  a  funnel-shaped  cavity 

in  the  ventral  surface  near  the  anterior  end,  called  the  vestibule 


dco 


Fig.  342.  —  Diagram  illustrating  the  anatomy  of  the  pharyngeal  region  of 
Amphioxus.  ao.y  dorsal  aorta;  atr.,  atrium;  d.co,  dorsal  coelom;  en.,  endostyle; 
ep.,  epipleur;  Jr.,  fin-ray;  go.,  gonads;  hy.,  hyperbranchial  groove;  mp.,  meta- 
pleur;  mpc,  metapleural  fold;  my.,  myotomes;  nch,  notochord;  nph,  nephrid- 
ium;  nt.,  neural  tube;  p.b.,  primary  gill-bar;  th.,  tongue-bar;  S.co,  subendo- 
stylar  coelom.     (From  Bourne.) 


(Fig.  341,  ves).  The  anus  {an.)  is  situated  on  the  left  side  of  the 
body  in  myotome  fifty- two  (w^^).  Just  in  front  of  the  ventral  fin 
opposite  myotome  thirty-six  {m^^)  is  the  atriopore  (atp.),  an  open- 
ing through  which  water  used  in  respiration  passes  to  the  outside. 


396  COLLEGE   ZOOLOGY 

Internal  Anatomy  and  Physiology.  —  Skeleton.  —  Am- 
phioxus  has  a  well-developed  axial  support,  the  notochord  (Figs. 
341-342,  nch),  lying  near  the  dorsal  surface  and  extending  almost 
the  entire  length  of  the  body.  The  notochord  is  composed  of 
vacuolated  cells  which  are  made  turgid  by  their  fluid  contents 
and  are,  therefore,  resistant.  Other  skeletal  structures  are  the 
connective  tissue  rods  which  form  the  fin-rays  (Fig.  341, /r.),  and 
similar  structures  (Fig.  343,  sk)  that  support  the  cirri  (cir)  of 
the  oral  hood  (or.fhd).- 

Digestive  System  (Fig.  343).  —  The  food  of  Amphioxus  con- 
sists of  minute  organisms  which  are  carried  into  the  mouth  with 
the  current  of  water  produced  by  cilia  on  the  gills  (compare  with 
mussel,  p.  246).  The  mouth  {mth)  is  an  opening  in  a  membrane, 
the  velum  (vl),  and  may  be  closed  by  circular  muscle  fibers  which 
surround  it.  Twelve  sensory-oral  or  velar  tentacles  (vl.t)  pro- 
tect the  mouth,  and,  when  folded  across  it,  act  as  a  strainer,  thus 
preventing  the  entrance  of  coarse,  solid  objects.  The  funnel- 
shaped  vestibule  is  the  cavity  of  the  oral  hood  (or.fhd).  The 
twenty-two  ciliated  cirri  (cir)  which  project  from  the  edge  of 
the  oral  hood  are  provided  with  sensory  cells.  The  inner  wall  of 
the  oral  hood  bears  a  number  of*  ciliated  lobes  and  is  known  as 
the  wheel  organ  because  its  cilia  appear  to  produce  a  rotatory 
movement.     Water  is  forced  into  the  mouth  by  the  cilia. 

The  mouth  opens  into  a  large,  laterally  compressed  pharynx 
(Fig.  343,  ph;  Fig.  342).  A  ciliated  dorsal  indentation  in  the 
pharynx  is  called  the  hyperbranchial  groove  (Fig.  342,  hy).  A 
ventral  groove,  the  endostyle  {en),  is  also  present.  The  endo- 
style  consists  of  a  median  ciliated  region  with  a  glandular  portion 
on  either  side.  The  glands  secrete  strings  of  mucus  (compare 
tunicate,  p.  391)  in  which  food  particles  are  entangled.  The 
cilia  then  drive  this  mucus  forward  by  way  of  two  peri- 
pharyngeal grooves  into  the  hyperbranchial  groove.  From  here 
it  is  carried  by  the  hyperpharyngeal  cilia  into  the  intestine  (Fig. 
343,  int).  A  ventral  finger-shaped  diverticulum  of  the  intestine 
is  known  as  the  liver  (Ir),  or  hepatic  ccecum,  since  it  is  supposed 


PHYLUM   CHORDATA 


397 


to  secrete  a  digestive  fluid  similar  to  that  produced  by  the  Uver 
in  the  vertebrates.     The  intestine  leads  directly  to  the  anus  {an). 


tttrp  \ 
int  coel 


vc/vL^r 


Fig.  343.  —  Diagram  of  the  anatomy  of  Amphioxus.  A,  anterior, 
B,  posterior  part,  an,  anus ;  atr,  atrium ;  alr^,  its  posterior  prolongation ; 
alrp,  atriopore ;  br,  brain ;  br.cl,  branchial  clefts ;  brf,  brown  funnel ; 
br.sep.i,  br.sep.2,  branchial  lamellae;  br.r.i,  br.r.2,  branchial  rods;  caud.f, 
caudal  fin;  cent.c,  central  canal;  cir,  cirri;  coel,  ccelom;  dors.f,  dorsal  fin; 
dors.f.r,  dorsal  fin-ray;  en  coe,  cerebral  vesicle;  e.sp,  eye  spot;  gon,  gonad; 
int,  intestine ;  Ir,  liver ;  mth,  mouth ;  myom,  myotomes ;  nch,  notochord ; 
nph,  -nephridia ;  olf.p,  olfactory  pit ;  or.f.hd,  oral  hood ;  ph,  pharynx ; 
sk,  skeleton  of  oral  hood  and  cirri  (dotted);  sp.cd,  spinal  cord;  vent.f,  ventral 
fin;  vent.f.r,  ventral  fin-ray;  vl,  velum;  vl.t,  velar  tentacles,  (From  the 
Cambridge  Natural  History,  after  Parker  and  Haswell.) 


Respiratory  System.  —  The  pharynx  (Fig.  343,  ph;  Fig. 
342)  is  attached  dorsally  and  hangs  down  into  a  cavity  called 
the  atrium  (Figs.  342-343,  atr.).    The  atriuna  is  not  the  ccelom 


398 


COLLEGE  ZOOLOGY 


but  is  lined  with  an  ectodermal  epithelium  and  is  really  external 
to  the  body,  as  has  been  proved  by  the  study  of  its  development. 
Water  which  is  carried  into  the  pharynx  by  way  of  the  mouth 
passes  through  the  gill-slits  into  the  atrium  and  out  of  the  atrio- 
pore  (Fig.  341,  atp ;  Fig.  343,  atrp).  The  gill-slits,  sometimes 
as  many  as  one  hundred  and  eighty,  are  separated  by  gill-bars 
(Fig.  342,  p.h.) ;  these  are  ciHated  and  supported  by  chitinous 
rods.  Respiration  takes  place  as  the  water,  driven  by  the  cilia, 
flows  through  the  gill-slits. 

Circulation.  —  Amphioxus  does  not  possess  a  heart.    The 
position  of  the  principal  blood-vessels  and  the  direction  of  the 


d.OLO 


tifSna. 


■sfhra  -' 
brcl 


^^m 


Ua-J 


fe\ffiii* 


afbra'    ^-"^  ^fbra. 


int 


hep. 2^ 
\hepport.v 


s.int  V 


Fig.  344.  —  Diagram  of  the  vascular  system,  oi  Amphioxus.  a/.6r.c,  afferent 
branchial  arteries ;  cp,  intestinal  capillaries ;  d.ao,  paired  dorsal  aortae ; 
d.ao,^  median  dorsal  aorta;  ef.br.a,  efferent  branchial  arteries;  hep.port.v., 
hepatic  portal  vein;  hep.v,  hepatic  vein;  «n/,  intestine;  /r,  liver;  ^A,  pharynx; 
s.int.v,  subintestinal  vein.     (From  Parker  and  Haswell.) 


blood  flow  are  shown  in  Figure  344.  The  subintestinal  vein 
(s.int.v)  collects  blood  loaded  with  nutriment  from  the  intes- 
tine (int)  and  carries  it  forward  into  the  hepatic  portal  vein  (hep. 
port.v),  and  thence  to  the  liver  (Ir).  The  hepatic  vein  (hep.v) 
leads  from  the  liver  to  the  ventral  aorta  (v.ao).  Blood  is  forced 
by  the  rhythmical  contractions  of  the  ventral  aorta  into  the  af- 
ferent branchial  arteries  (af.br. a),  which  are  situated  in  the  gill- 
bars,  and  then  through  the  efferent  branchial  arteries  (ef.br.a) 
into  the  paired  dorsal  aortae  (d.ao).  It  passes  back  into  the 
median  dorsal  aorta  (d.ao^)  and  finally  byway  of  intestinal  capil- 
laries (cp)  into   the  subintestinal  vein  (s.int.v).      The  blood  is 


PHYLUM    CHORDATA 


399 


oxygenated  during  its  passage  through  the  branchial  arteries. 
The  direction  of  the  blood  flow,  backward  in  the  dorsal  and  for- 
ward in  the  ventral  vessel,  is  like  that  of  the  vertebrates  (p.  407), 
but  just  the  reverse  of  that  in  annelids  and  arthropods  (see  pp. 
221  and  283). 

The  Ccelom.  —  The  coelom  arises  from  five  embryonic  pouches 
of  the  primitive  digestive  tract  *as  in  Balanoglossus  (p.  388),  but 
is  difiicult  to  make  out  in  the  adult.  The  position  of  the  ccelomic 
cavities  is  shown  in  Fig.  343,  coel,  and  Fig.  342,  d.co. 

Excretory  System.  —  The  excretory  organs  are  ciliated 
nephridia  (Figs.  342-343,  nph)  situated  near  the  dorsal  region 
of  the  pharynx.     The  nephridia  connect  the  dorsal  ccelom  (Fig. 

342,  d.co)  with  the  atrial  cavity.     A  pair  of  brown  funnels  (Fig. 

343,  hr.f)y  one  on  either  side  and  dorsal  to  the  intestine  in  the 
region  of  myotome  twenty-seven,  may  also  be  excretory  organs. 

Nervous  System.  —  Amphioxus  possesses  a  central  nerve-cord 
(Fig.  343,  sp.cd ;  Fig.  342,  nt)  lying  entirely  above  the  alimen- 
tary canal  (compare  anneUds,  p.  216,  and  arthropods,  p.  285). 
It  rests  on  the  notochord  and  is  almost  as  long.  A  minute  canal 
(Fig.  343  cent.c)  traverses  its  entire  length  and  enlarges  at  the 
anterior  end  into  a  cerebral  vesicle  (en.coe)  which  is  the  only  trace 
of  a  brain  present.  An  olfactory  pit  (olf.p)  opens  into  this 
vesicle  in  young  specimens.  At  the  anterior  end  of  the  nerve- 
cord  is  a  mass  of  pigmented  cells  forming  an  eye-spot  (e.sp). 
Two  pairs  of  sensory  nerves  arise  from'  the  cerebral  vesicle,  and 
supply  the  anterior  region  of  the  body.  The  rest  of  the  nerve- 
cord  gives  off  nerves  on  opposite  sides,  but  alternating  with  one 
another.  These  nerv^es  are  of  two  kinds:  (i)  dorsal  nerves  with 
a  sensory  function  which  pass  to  the  skin,  and  (2)  ventral  nerves 
with  a  motor  function  which  enter  the  myotomes.  The  sense- 
organs  include  the  olfactory  pit,  eye-spot,  and  sensory  cells  in 
the  ectoderm,  on  the  cirri,  and  on  the  velar  tentacles. 

Reproduction.  —  In  Amphioxus  the  sexes  are  separate. 
The  twenty-six  pairs  of  gonads  (Fig.  341,  g^,  g^e.  pjg  ^^2,  go) 
project  into  the  atrium.     The  germ-cells  are  discharged  into  the 


400  COLLEGE  ZOOLOGY 

atrial  cavity  and  reach  the  exterior  through  the  atriopore.  Fer- 
tilization takes  place  in  the  water.  The  early  development  of 
the  egg  of  Amphioxus  was  described  in  Chapter  III  (pp.  87  to  89), 
and  is  illustrated  in  Figure  51.  For  a  detailed  description  of  the 
embryology  of  Amphioxus,  the  student  is  referred  to  Willey's 
Amphioxus  and  the  Ancestry  of  the  Vertebrates  and  to  advanced 
text-books  of  zoology. 

4.   SuBPHYLUM  IV.    Vertebrata:   Introduction 

The  Vertebrata  are  animals  with  an  axial  notochord  at  some 
period  in  their  existence.  This  notochord  persists  in  some  of 
the  lower  vertebrates,  but  is  modified  by  an  investment  of  carti- 
lage which  becomes  segmented  and  constitutes  the  vertebral  col- 
umn. In  the  higher  vertebrates  the  vertebral  column  is  made  up 
of  a  series  of  bodies  called  vertebrae,  and  the  notochord  disappears 
before  the  adult  stage  is  reached.  The  vertebrates  are  the  lam- 
preys, hags,  sharks,  rays,  chimaeras,  fishes,  frogs,  toads,  sala- 
manders, lizards,  snakes,  crocodiles,  turtles,  birds,  hairy  quadru- 
peds, whales,  seals,  bats,  monkeys,  and  man.  Seven  classes  of 
vertebrates  are  recognized. 

Class  I.  Cyclostomata  (Gr.  kyklos,  circle;  stoma,  mouth).  — 
Lampreys  and  Hags  (Figs.  352-356).  —  Cold-blooded,  fish-like 
vertebrates  without  jaws  and  lateral  fins. 

Class  II.  Elasmobranchii  (Gr.  elasmos,  metal  plate;  bran- 
chia,  gills).  —  Sharks,  Rays,  and  Chimeras  (Figs.  358-367). — 
Cold-blooded,  fish-like  vertebrates  with  jaws,  a  cartilaginous 
skeleton,  a  persistent  notochord,  and  placoid  scales. 

Class  III.  Pisces  (Lat.  piscis,  fish). — Fishes  (Figs.  368- 
408).  —  Cold-blooded  vertebrates  with  jaws,  and  usually  with 
lateral  fins  supported  by  fin-rays.     They  breathe  chiefly  by  gills. 

Class  IV.  Amphibia  (Gr.  amphi,  both;  bios,  life).  —  Frogs, 
Toads,  and  Salamanders  (Fig^.  409-438). —  Cold-blooded, 
naked  vertebrates  mostly  with  pentadactyle  (five- fingered) 
limbs.  The  young  are  usually  aquatic  and  breathe  by  gills ;  the 
adults  usually  lose  the  gills,  and  breathe  by  means  of  lungs. 


V 


PHYLUM  CHORDATA 


401 


Class  V.  Reptilia  (Lat.  repere,  to  crawl).  —  Sphenodon, 
Chameleons,  Lizards,  Snakes,  Crocodiles,  and  Turtles 
(Figs.  439-469).  —  Cold-blooded  vertebrates  breathing  by  means 
of  lungs  and  usually  having  a  scaly  skin. 

Class  VI.  AvES  (Lat.  avis,  bird).  —  Birds  (Figs.  470-509).  — 
Warm-blooded  vertebrates  with  the  fore  limbs  modified  into 
wings  and  the  body  covered  with  feathers. 

Class  VII.  Mammalia  (Lat.  mamma,  breast).  — Hairy  Quad- 
rupeds, Whales,  Seals,  Bats,  Monkeys,  and  Man  (Figs.  510- 
550). — Warm-blooded  vertebrates  with  a  hairy  covering  at 
some  stage  in  their  existence;  the  young  nourished  after  birth 
by  the  secretion  of  the  mammary  glands  of  the  mother. 

Plan   of   Structure.  —  The   vertebrates    resemble    the   other 
chordates  in  their  metamerism  and  bilateral  symmetry  and  in  the 
NEURALTUBE/'  CEREBRO  spina  l  canal) 
SPINAL  CORD                       >C               NOTOCHORD      VISCERAL  TUBCCCOfZ 
BRAIN,  A  .   >  . .y     Z.a^i.i.7>> ^.    .  . L 


ORALCAVI 

INTERNAL  GILL  SLITS, 

HEART 


CLOACA 


URINARY  BlaOOLR 


I8ILE  DUCT 
PANCREAS 

Fig.  345.  —  Diagrammatic  longitudinal  section  of  a  vertebrate  (female). 

(From  Wiedersheim.) 


possession  of  a  ccelom,  a  notockord,  and  gill-slits  at  some  stage 
in  their  existence,  and  a  dorsal  nerve  tube.  They  differ  from  other 
chordates  and  resemble  one  another  in  the  possession  of  carti- 
laginous or  bony  vertebrce,  usually  two  pairs  of  jointed  appendages 
containing  a  central  skeleton,  a  ventrally  situated  heart  with  at 
least  two  chambers,  and  red  corpuscles  in  the  blood. 


402 


COLLEGE  ZOOLOGY 


chna 


pr*         vivb 


ctcto 


The  body  of  a  vertebrate  may  be  divided  into  a  head^  neck 
(usually),  and  trunk.  In  many  species  there  is  a  posterior  ex- 
tension, the  tail.  Two  pairs  of  lateral  appendages  are  generally 
present,  the  thoracic  (pectoral  fins,  forelegs,  wings,  or  arms) 
and  the  pelvic  (pelvic  fins,  hind  legs).  The  limbs  support  the 
body,  are  locomotory,  and  usually  have  other  special  functions. 

A  general  account 
of  the  plan  of  struc- 
ture of  an  ideal  ver- 
tebrate can  be  given 
most  clearly  with 
the  aid  of  diagrams 
showing  longitudi- 
nal and  cross  sec- 
tions through  the 
body  (Figs.  345- 
346).  As  in  Am- 
phioxus,  the  nerve 
cord  {sp.c)  is  dorsal 
but  extends  in  front 
of  the  end  of  the 
notochord  and  en- 
larges into  a  brain. 
The  notochord  be- 
comes invested  by 
the  vertebrae  (Fig. 
346,  cw).  The  C(s/ow  (coe/)  is  large.  The  alimentary  canaliorms 
a  more  or  less  convoluted  tube  (int)  which  Hes  in  the  body 
cavity.  The  liver,  pancreas,  and  spleen  are  situated  near  the 
alimentary  canal.  In  the  anterior  trunk  region  are  the  lungs 
and  heart.  The  kidneys  (ms.nph)  and  gonads  (gon)  lie  above 
the  alimentary  canal. 

Integument  (Fig.  347). — The  outer  covering  of  the  verte- 
brates is  the  skin,  consisting  of  an  outer  ectodermal  layer,  the 
epidermis  {Sc,SM),j3ind  an  inner  mesodermal  layer,  the  dermis 


Fig.  346.  —  Transverse  section  through  the  trunk 
of  a  vertebrate,  en,  centrum  of  vertebra;  coel,  ccelom; 
crd.v,  cardinal  vein;  d.ao,  dorsal  aorta;  d.f,  dorsal 
fin;  d.m,  dorsal  muscles;  f.r,  fin-ray;  gon,  gonad; 
int,  intestine;  l.v,  lateral  vein;  mes,  mesentery; 
ms.n.d,  mesonephric  duct  ;  ms.nph,  mesonephros; 
na,  neural  arch;  p.n.d,  pronephric  duct;  pr,  peri- 
toneum, parietal  layer;  pr',  visceral  layer;  r,  sub- 
peritoneal rib;  r',  intermuscular  rib;  sp.c,  spinal 
cord;  t.p,  transverse  process;  v.m,  ventral  muscles. 
(From  Parker  and  Haswell.) 


PHYLUM   CHORDATA 


403 


(Co).  The  skin  is  chiefly  protective  and  sensory,  but  may  also 
carry  on  respiration  and  excretion.  Excretion  takes  place  by 
means  of  glands,  which  may  be  simple,  as  the  mucous  glands  of 
fishes,  or  complex,  as  the  sweat,  oil,  and  mammary  glands.  The 
skin  often  produces  numerous 
outgrowths  such  as  hair,  feathers, 
nails,  hoofs,  claws,  scales,  teetl^, 
and  bony  plates. 

Skeleton.  —  The  outgrowths 
of  the  integument  noted  above 
constitute  the  exoskeleton.  The 
internal  supporting  framework 
of  the  body  is  the  endoskeleton. 
This  consists  of  (i)  an  axial 
portion  comprising  the  skull  and 
vertebral    column,   and    (2)    an 

.  Fig.  347. — Section  through  human 

appendicular   portion  which  sup-     skin.      Co,  dermis ;    F,  subcutaneous 

ports  the  appendages.  ^ ^t ;  GP,  vascular  papillae ;  H,  hair  with 

^,       ,  r    1  111  sebaceous  glands  (D);    iV,  G,  nerves; 

1  he  6owe5  of  the  endoskeleton    ^^^    sensory    papilla;    Sc,    stratum 

corneum ;  SD,  sweat-glands  with 
their  ducts  {SD') ;  SM,  stratum  mal- 
pighi.     (From  Wiedersheim.) 


are  typically  formed  in  and 
around  cartilage.  The  animal 
part  of  the  bone  is  the  cartilage; 

this  can  be  obtained  by  dissolving  out  the  mineral  part,  the  bone- 
ash,  in  hydrochloric  acid.  The  bone-ash  consists  principally  of 
carbonate  and  phosphate  of  lime,  and  is  the  residue  when  a  bone 
is  burned.  The  mineral  constituents  give  the  bone  rigidity; 
the  cartilage  furnishes  plianc^  and  elasticity.  Bones  support 
the  soft  parts,  furnish  points  of  attachment  for  the  muscles,  and 
protect  certain  delicate  organs,  such  as  the  brain,  spinal  cord, 
and  eyes. 

The  axial  skeleton  consists  typically  of  the  skull,  the  vertebrae, 
and  the  ribs  which  may  be  attached  to  a  ventral  bone,  the 
sternum.  The  skull  includes  a  brain  case  or  cranium,  which 
protects  the  brain,  and  a  visceral  skeleton,  which  supports  the 
respiratory  apparatus  and  includes  the  facial  bones. 


404 


COLLEGE  ZOOLOGY 


The  vertebral  column  serves  as  a  supporting  axis  for  the  body. 
Its  structure,  however,  is  such  as  to  allow  movement,  since  it 
is  composed  of  a  number  of  movable  parts,  the  vertehrce.  The 
vertebrae  develop  from  cartilaginous  tissue  which  forms  a 
sheath  around  the  notochord.     A  typical  vertebra  consists  of 


mt 


ph/ 


HI 


Fig.  348.  —  Diagrams  of  A,  fore  limb  and  girdle,  and  B,  hind  limb  and  girdle 
of  a  vertebrate.  I-V,  digits;  ac/6,  acetabulum;  C L,  clavicle;  cn.i,  en. 2,  cen- 
tralia;  COR,  coracoid  ;  dst.  1-5,  distalia;  F E,  femur;  FI,  fibula;  fi,  fibulare; 
gl,  glenoid  cavity;  HU,  humerus;  I L,  ilium;  int,  intermedium;  IS,  ischium; 
mtcp.1-5,  metacarpals ;  inUs.1-5,  metatarsals;  p.cor,  procoracoid ;  ph,  pha- 
langes;  PU,  pubis;  RA,  radius;  ra,  radiale;  SCP,  scapula;  TI,  tibia; 
ti,  tibiale;    U L,  ulna;   ul,  ulnare.     (From  Parker  and  Haswell.) 


a  supporting  basal  portion,  the  centrum  (Fig.  346,  en),  a  dorsal 
or  neural  arch  (na),  which  protects  the  spinal  cord  (sp.c),  a 
neural  spine,  which  extends  dorsally  from  the  center  of  the 
neural  arch  and  serves  for  the  attachment  of  muscles,  and  a 
transverse  process  (t.p)  on  each  side  of  the  centrum  to  which  a  rib 
(r)  may  be  joined. 


PHYLUM   CHORDATA  405 

Four  ivi)es  of  vertebrce  are  recognized;  (i)  cervical  vertebrcB  in 
the  neck,  (2)  dorsal  or  thoracic  vertebrce  which  bear  ribs,  (3) 
sacral  vertebrce  with  which  the  skeleton  of  the  hind  limbs  are 
united,  and  (4)  caudal  vertebrcB  posterior  to  the  sacrum.  The 
ribs  support  the  walls  of  the  trunk  and  may  be  united  with  a 
plate-like  breast-bone,  the  sternw^.  Ribs  that  are  not  attached 
to  the  sternum  are  called  false  ribs. 

The  appendicular  skeleton  serves  to  support  the  appendages 
and  fasten  them  to  the  axial  skeleton.  The  anterior  appendages 
are  joined  to  the  pectoral  girdle ;  the  posterior  appendages  to  the 
pelvic  girdle.  The  bones  of  these  girdles  and  of  the  appendages 
are  shown  in  Figure  348.  The  appendicular  skeleton  of  fishes 
is  usually  more  simple  than  that  of  the  higher  vertebrates. 

Muscular  System.^  —  The  "  flesh  "  of  the  vertebrates  con- 
sists largely  of  muscle.  Muscular  tissue  is  capable  of  contraction 
and  is  responsible  for  all  the  movements  of  an  animal.  The 
muscles  are  attached  to  the  bones  by  tendons.  The  body 
muscles  are  called  axial,  those  of  the  appendages,  appendicular. 
The  muscles  of  the  internal  organs  are  involuntary,  i.e.  they 
do  not  depend  upon  the  will  of  the  animal  (see  p.  74). 

Digestive  System.  — The  organs  of  digestion  vary  considerably 
among  the  vertebrates.  The  mouth  opens  into  a  buccal  cavity 
which  is  usually  provided  with,  jaws  generally  bearing  teeth.  The 
teeth  are  used  to  hold  the  food  and  often  to  masticate  it.  In. 
many  cases  a  fluid  from  salivary  glands  enters  the  buccal  cavity 
and  is  there  mixed  with  the  food,  making  it  easier  to  swallow  and 
digest.  Following  the  buccal  cavity  is  the  pharynx.  In  lower 
vertebrates  and  in  the  embryos  of  higher  forms  the  pharynx  opens 
to  the  outside  by  gill-slits.  The  oesophagus  leads  from  the  pharynx 
to  the  stomach.  It  is  usually  a  narrow  tube,  but  may  be  en- 
larged as  in  birds,  to  form  a  crop  for  storing  and  softening  food. 

The  stomach  varies  in  shape  and  structure  according  to  the 
kind  of  food  to  be  digested  in  it.     Its  walls  contain  glands  which 

1  A  general  account  of  the  systems  of  organs  and  their  functions  will  be  found  on 
pages  76  to  79. 


4o6  COLLEGE  ZOOLOGY 

secrete  digestive  ferments  or  enzymes  (p.  220)  and  hydro- 
chloric acid;  these  help  dissolve  the  food  so  that  it  can  be 
absorbed.  A  circular  muscle,  called  the  pyloric  sphincter,  regu- 
lates the  passage  of  food  into  the  small  intestine. 

Connected  with  the  small  intestine  by  a  bile  duct  is  the  liver. 
This  organ  secretes  an  alkaline  fluid  called  bile  which  is  poured 
into  the  intestine,  where  it  divides  fatty  food  into  particles  fine 
enough  to  penetrate  the  walls  of  the  intestine.  Often  an  en- 
largement, the  gall-bladder,  is  present,  in  which  the  bile  is  stored. 
The  liver  also  changes  sugar  into  a  substance  called  glycogen, 
which  is  stored  up  as  a  reserve  for  the  future  needs  of  the  animal. 

Another  large  gland,  the  pancreas,  secretes  a  digestive  fluid, 
the  pancreatic  juice,  w^hich  enters  the  intestine  through  the 
pancreatic  duct.  This  fluid  contains  three  important  ferments; 
(i)  amylopsin,  which  forms  soluble  sugar  from  starch,  (2)  trypsin, 
which  converts  proteid  into  peptones,  and  (3)  steapsin,  which 
changes  fat  into  soluble  fatty  acids  and  glycerin. 

The  intestine  is  usually  longer  than  the  body  and  therefore 
coiled  within  the  abdomen.  Through  its  walls  most  of  the  di- 
gested food  is  absorbed  into  lymphatic  tubes  and  blood  capil- 
laries. The  absorbent  surface  is  often  increased  by  folds  and 
small  prominences  called  villi.  Undigested  particles  are  formed 
into  fcBces  in  the  posterior  part  of  the  intestine  and  ejected 
through  the  anus.  In  many  vertebrates  the  intestine  opens 
into  a  terminal  sac,  the  cloaca,  into  which  the  excretory  and 
reproductive  ducts  also  open. 

Circulatory  System.  —  The  blood  into  which  the  digested 
food  passes  from  the  alimentary  canal  consists  of  a  colorless 
plasma  containing  passive  red  corpuscles  and  active,  ameboid, 
colorless  corpuscles.  The  color  of  the  red  corpuscles  is  due  to 
the  presence  of  a  substance  called  hcemoglobin.  The  heart  of 
vertebrates  hes  in  a  part  of  the  coelom  termed  the  pericardium. 
It  consists  of  at  least  two  chambers:  (i)  an  auricle  into  which 
the  blood  is  brought  by  the  veins,  and  (2)  a  ventricle  which  forces 
the  blood  through  the  arteries. 


PHYLUM   CHORDATA  407 

The  smallest  blood  vessels  are  called  capillaries.  The  ex- 
change of  substances  between  the  blood  and  tissues  takes  place 
through  the  walls  of  the  capillaries.  Certain  capillaries  unite 
to  form  veins ^  which  carry  blood  from  all  parts  of  the  body  to  the 
heart.  Arterial  blood  leaves  the  heart  chiefly  through  the  aorta. 
The  aorta  gives  off  branches  which  in  turn  branch  imtil  they  end 
in  minute  arterial  capillaries.  Tne  functions  of  the  circulatory 
system  are  like  those  of  this  system  in  invertebrates,  i.e.  the 
transportation  of  nutriment,  oxygen,  and  waste  products  from 
one  part  of  the  body  to  another.  In  close  connection  with  the 
circulatory  system  are  a  number  of  spaces  and  channels  com- 
prising the  lymphatic  system.  Lymph  is  a  clear  fluid  containing 
ameboid  cells  like  the  colorless  blood  corpuscles. 

Respiratory  System.  —  Two  kinds  of  respiration  may  be 
recognized,  (i)  external  respiration,  during  which  oxygen  passes 
into  the  blood  from  the  air  or  water  and  carbon  dioxide  passes 
out  of  the  blood,  and  (2)  internal  respiration,  during  which  the 
blood  supplies  oxygen  to  and  takes  carbon  dioxide  from  the 
cells  of  the  body.  External  respiration  is  carried  on  by  gills  in 
most  aquatic  vertebrates  and  by  lungs  in  terrestrial  vertebrates. 
Respiration  also  takes  place  to  some  extent  through  the  skin. 
Oxygen  unites  readily  with  the  haemoglobin  in  the  red  corpuscles. 
The  haemoglobin  is  then  transported  by  the  blood  from  the 
respiratory  organs  to  the  capillaries,  where  it  breaks  up,  the 
oxygen  being  absorbed  by  the  tissues.  Carbon  dioxide  from  the 
tissues  becomes  chemically  combined  with  the  sodium  in  the  blood, 
is  carried  to  the  respiratory  organs,  and  discharged  to  the  outside. 

Excretory  System.  —  The  substances  resulting  from  the  oxi- 
dation of  protoplasm  are  eliminated  by  the  kidneys,  respiratory 
organs,  and  skin.  These  waste  products  are  carried  by  the  blood. 
Carbon  dioxide  is  eliminated  by  the  respiratory  organs.  Ni- 
trogenous waste  products  are  excreted  by  the  kidneys  in  the  form 
of  urea  or  uric  acid.  Ducts,  called  ureters,  lead  from  the  kidneys 
either  directly  to  the  outside  or  empty  the  excretion  into  a 
storage  vesicle,  the  urinary  bladder. 


4o8 


COLLEGE  ZOOLOGY 


Nervous  System.  —  The  nervous  system  of  vertebrates  is 
more  complex  than  that  of  any  other  animals.  It  comprises  a 
central  nervous  system  consisting  of  the  hrain  and  spinal  cord, 
a  peripheral  nervous  system  consisting  of  the  cerebral  and  spinal 
nerves,  and  a  sympathetic  system.  The  brain  is  made  up  of  three 
primary  vesicles,  a  fore-brain,  mid-brain,  and  hind-brain.  The 
fore-brain  is  thought  to  correspond  to  the  cerebral  vesicle  of 


Fig.  349.  —  Diagram  of  the  spinal  cord  showing  the  paths  taken  by  nervous 
impulses.  The  direction  of  the  impulses  is  indicated  by  arrows,  c.c,  central 
canal;  col,  collateral  fibers;  c.cori,  cell  in  the  cerebral  cortex;  eg,  smaller 
cerebral  cell;  d.c,  cells  in  dorsal  horn  of  gray  matter;  d.r,  dorsal  root;  g,  gan- 
glion of  dorsal  root;  g.c,  ganglion  cell  in  dorsal  ganglion;  g.m,  gray  matter; 
M,  muscle;  m.c,  cell  in  medulla  oblongata;  tn.f,  motor  fiber;  S,  skin;  s.f,  sen- 
sory fiber;  sp.c,  spinal  cord;  v.c,  cells  in  ventral  horn  of  gray  matter; 
v.r,  ventral  root;    w.m,  white  matter.     (From  Holmes,  after  Parker.) 


Amphioxus  (Fig.  343,  br).  The  fore-brain  usually  gives  rise  to  a 
pair  of  cerebral  hemispheres,  the  mid-brain  to  a  pair  of  optic  lobes, 
and  the  hind-brain  to  the  cerebellum  and  medulla  oblongata. 
The  spinal  cord  is  a  thick  tube  directly  connected  with  the  brain ; 
it  passes  through  the  neural  arches  of  the  vertebral  column. 

The  peripheral  nervous  system  consists  of  ten  to  twelve  pairs 
of  cranial  nerves  and  a  number  of  pairs  of  spinal  nerves.  The 
origin,  distribution,  and  function  of  the  cranial  nerves  are 
indicated  in  Table  XIV. 

The  spinal  nerves  arise  from  the  spinal  cord  in  pairs,  one  on 


PHYLUM  CHORD ATA 


409 


TABLE  XIV 

THE  NUMBER,  NAMES,  ORIGIN,  DISTRIBUTION,  AND  FUNCTIONS  OF  THE 
CRANIAL  NERVES   OF  VERTEBRATES 


Number 

Name 

Origin 

Distribution 

Function 

I 

Olfactory 

Olfactory 
lobe       of 
fore-brain 

'  Lining  of  nose 

Sensory 

II 

Optic 

Second  vesi- 
cle of  fore- 
brain 

Retina  of  eye 

Sensory 

III 

Oculomotor 

Ventral  re- 
gion      of 
mid-brain 

Muscles  of  eye 

Motor 

IV 

Trochlearis 

Dorsal    re- 

Superior oblique 

Motor 

(patheticus) 

gion  of  the 
mid-brain 

muscle  of  eye 

V 

Trigeminal 

Side  of  me- 

Skin of  face,  mouth. 

Largely 

(trifacial) 

dulla 
(hind- 
brain) 

and    tongue,    and 
muscles  of  jaws 

sensory 

VI 

Abducens 

Ventral  re- 
gion      of 
medulla 

External  rectus 
muscle  of  eye 

Motor 

VII 

Facial 

Side  of  me- 

Chiefly to  muscles  of 

Largely 

dulla 

face 

motor 

VIII 

Auditory 

Side  of  me- 
dulla 

Inner  ear 

Sensory 

IX 

Glossopharyn- 

Side of  me- 

Muscles  and   mem- 

Sensory 

geal 

dulla 

branes  of  pharynx, 
and  tongue 

and 
motor 

X 

Vagus  (pneu- 

Side  of  me- 

Posterior      visceral 

Sensory 

mogastric) 

dulla 

arches,  lungs,  heart, 
stomach  and*  intes- 
tines 

and 
motor 

XI 

Spinal   acces- 

Side of  me- 

Chiefly muscles  of 

Sensory 

sory      (not 

dulla 

shoulder 

and 

present    in 

motor 

all      verte- 

brates) 

XII 

Hypoglossal 

Ventral  re- 

Muscles   of    tongue 

Motor 

(not  present 

gion       of 

and  neck 

in  all  verte- 

medulla 

. 

brates) 

4IO  COLLEGE  ZOOLOGY 

either  side  in  each  body  segment,  and  pass  out  between  the  ver- 
tebrae. Each  nerve  has  two  roots  (Fig.  349),  a  dorsal  root  (d.r) 
and  a  ventral  root  (v.r).  The  dorsal  root  possesses  a  ganglion 
(g)  containing  nerve  cells  (g.c).  Its  fibers  carry  impulses  tow- 
ard the  spinal  cord  from  various  parts  of  the  body  and  are 
therefore  sensory.  The  fibers  of  the  ventral  root  carry  impulses 
from  the  spinal  cord  to  the  tissues  and  are  therefore  motor.  The 
constitution  of  the  nerve  cells  (neurons)  is  similar  to  that  of  the 
earthworm  (p.  225).  The  direction  of  the  nervous  impulses  is 
indicated  by  arrows  in  Figure  349. 

On  each  side  of  the  spinal  cord  is  a  chain  of  ganglia  which  is 
connected  at  various  places  with  the  central  nervous  system. 
This  is  known  as  the  sympathetic  nervous  system.  These  ganglia 
send  nerves  chiefly  to  the  alimentary  tract,  circulatory  system, 
and  glandular  organs. 

Sense-Organs.  —  Vertebrates  possess  a  number  of  highly 
developed  sense-organs  —  nose,  eyes,  and  ears.  In  addition  to 
these  there  are  many  species  with  sense-cells,  single  or  in  groups, 
scattered  over  the  body^  In  some  of  the  lower  vertebrates  these 
take  the  form  of  lateral  line  organs  (p.  427)  of  doubtful  function. 
Usually  sense-organs  of  taste  occur  as  pits  over  the  tongue  and 
soft  palate. 

The  sense-organs  of  smell  are  located  in  the  nose.  The  nose 
consists  of  a  pair  of  cavities  at  the  anterior  end  of  the  body. 
These  cavities  are  lined  with  folds  of  mucous  epithelium  covered 
with  olfactory  sense-cells. 

The  two  ears  of  vertebrates  arise  as  cavities  of  the  skin  at 
the  sides  of  the  midbrain.  They  are  rather  complicated  in 
structure,  as  indicated  in  Figure  350.  They  function  as  organs 
of  hearing  and  equilibrium. 

The  internal  ear  is  called  the  membranous  labyrinth  and  is 
enclosed  by  cartilage  or  bone.  Within  the  labyrinth  is  a  fluid 
called  endolymph;  and  between  the  labyrinth  and  the  sur- 
rounding cartilage  or  bone  is  a  fluid  called  perilymph.  The 
labyrinth  is  usually  constricted  into  two  chambers,  (i)  a  dorsal 


PHYLUM   CHORDATA 


411 


utriculus  (Fig.  350,  u)  which  gives  rise  to  three  semicircular 
canals  (ca,  ce,  cp),  and  (2)  a  ventral  sacculus  (s)  bearing  an  out- 
growth called  the  cochlea  (/).  The  bases  of  the  semicircular 
canals  are  enlarged  into  ampullce  {aa,  ae,  ap)  containing  cells 
with  long  sense  hairs  which  record  change  of  position  in  any 
direction  and  are  therefore  organs  of 
equilibrium.  The  cochlea  of  the^  sac- 
culus in  higher  vertebrates  is  well 
developed,  contains  the  auditory  sense- 
cells,  and  is  the  true  organ  of  hearing. 

Sound  waves  are  brought  to  the 
cochlea  in  the  ears  of  higher  vertebrates 
by  means  of  the  middle  ear.  This  con- 
sists pi  a  vibrating  membrane,  the 
tympanum,  which  transmits  vibrations 
to  the  inner  ear  with  the  aid  of  a  chain 
of  three  bones. 

In  many  vertebrates  a  funnel-shaped 
fold  of  skin,  which  is  supported  by 
cartilage,  and  called  the  pinna  or  ex- 
ternal ear,  aids  in  catching  sound  waves. 
In  aquatic  animals  this  collecting  ap- 
paratus is  not  necessary,  since  the 
water  carries  the  sound  waves  to  the 
tissues  which  transmit  them  directly 
to  the  inner  ear. 

The  eyes  are  the  most  complex  of 
the  sense-organs  of  vertebrates.  They 
arise  in  part  from  the  sides  of  the  fore- 
brain  and  in  part  from  the  skin  and  connective  tissue.  The 
principal  elements  of  structure  and  the  method  of  action  may  be 
pointed  out  by  means  of  a  diagram  of  the  human  eye  (Fig.  351). 
The  eye  is  nearly  spherical.  It  consists  of  three  concentric  coats 
enclosing  transparent  substances.  The  outer  or  sclerotic  coat  {Set) 
is  the  white  of  the  eye.     It  is  composed  of  connective  tissue  and 


Fig.  350.  —  Semidiagram- 
matic  figure  of  the  left 
membranous  labyrinth  of  a 
vertebrate,  aa,  ae,  ap,  am- 
pullae of  semicircular  canals; 
ass,  apex  of  sinus  utriculi 
superior;  ca,  ce,  cp,  anterior, 
external,  and  posterior  semi- 
circular canals;  cus,  utriculo- 
saccular canal;  de,se,  ductus 
and  saccus  endolymphaticus; 
/,  recessus  sacculi;  rec,  re- 
cessus  utriculi;  s,  sacculus; 
sp,  sinus  utriculi  posterior; 
ss,  sinus  utriculi  superior; 
u,  utriculus.  (From  Wieders- 
heim.) 


412 


COLLEGE  ZOOLOGY 


serves  as  a  protective  covering.  In  front  of  the  lens  (L)  the 
sclerotic  coat  forms  a  transparent  area  called  the  cornea  (c). 
Beneath  the  sclerotic  coat  is  the  middle  coat  or  choroid  (Ch) ; 
this  is  supplied  with  blood  vessels  and  contains  a  great  deal  of 

black  pigment  {P.E) 
which  prevents  light 
from  entering  except 
through  the  cornea. 
The  choroid  coat  is 
separated  from  the 
sclerotic  coat  and  perfo- 
rated just  in  front  of  the 
lens;  the  opening  is  the 
pupil,  and  a  part  of 
the  choroid  surrounding 
the  pupil  is  the  iris  (/). 
The  inner  coat,  the 
retina  (R),  is  the  most 
important,  since  it  is  the 
sensitive  layer,  being  an 
expansion  of  the  optic 
nerve  (O.N).  It  lines 
the  cavity  back  of  the 
lens.  The  lens  (L)  is 
biconvex  and  trans- 
parent. It  is  attached 
to  the  choroid  coat  by 
a  suspensory  ligament 
(sp.  I) ,  and  separates  the 
small  anterior  cavity,  filled  with  a  fluid  called  aqueous  humor, 
from  the  large  posterior  cavity,  filled  with  a  jelly-like  substance 
called  vitreous  humor  {V.H.). 

The  eye  is  like  a  camera  in  certain  respects.  With  the  aid 
of  the  lens  an  image  is  formed  on  the  sensitive  retina  of  the 
objects  in  front  of  the  cornea.     The  eye  is  accommodated  for 


Fig.  351.  —  Diagrammatic  horizontal  section 
of  the  eye  of  Man.  c,  cornea;  Ch,  choroid 
(dotted);  C.P.,  ciliary  processes;  ex,  epithelium 
of  cornea;  e.cj,  conjunctiva;  f.o,  yellow  spot; 
/,  iris ;  L,  lens ;  O.N,  optic  nerve ;  os,  ora 
serrata;  o-x,  optic  axis;  p.c.R,  anterior  non- 
visual  portion  of.  retina;  P.E,  pigmented 
epithelium  (black);  R,  retina;  sp.l,  suspen- 
sory ligament;  Scl,  sclerotic;  V.H.,  vitreous 
chamber.  (From  Parker  and  Haswell,  after 
Foster  and  Shore.) 


PHYLUM   CHORDATA 


413 


recording  images  of  distant  and  near  objects  by  changes  in  the 
convexity  of  the  lens  caused  by  its  own  elasticity,  and  the  pull 
exerted  upon  it  by  the  elastic  choroid  coat  and  the  ciliary 
muscles  {C.P.).  In  viewing  near  objects  the  ciliary  muscle 
counteracts  the  pull  of  the  choroid  coat  and  allows  the  lens  to 
assume  a  more  convex  shape,  whereas  distant  objects  are  made 
distinct  by  the  flattening  of  the  Jens. 

The  eye  is  moved  by  six  muscles;  four  straight  {rectus)  and 
two  oblique.  Folds  of  skin,  the  eyelids,  protect  the  eye  in  higher 
vertebrates.  There  may  be  three  eyelids :  an  upper  and  a  lower 
lid  which  act  vertically,  and  a  lateral  lid  (nictitating  membrane) 
which  moves  outward  from  the  inner  angle  of  the  eye.  In  some 
reptiles  the  eyelids  are  transparent  and  fused  over  the  eye. 
Terrestrial  vertebrates  have  lacrymal  glands  in  connection  with 
the  eye,  the  secretion  from  which  keeps  the  surface  of  the  eye- 
ball moist  and  washes  away  foreign  particles. 

Reproductive  System.  —  The  sexes  of  vertebrates,  with  few 
exceptions,  are  separate.  The  reproductive  organs  arise  in 
close  connection  with  the  excretory  organs,  and  the  excretory 
ducts  may  serve  to  carry  germ-cells  to  the  exterior.  Fertiliza- 
tion takes  place  in  some  Amphibia  and  most  fishes  after  the 
eggs  are  extruded.  In  other  vertebrates  fertilization  is  internal. 
Most  vertebrates  lay  eggs,  i.e.  are  oviparous,  but  many  of  them, 
especially  mammals,  bring  forth  their  young  alive,  i.e.  are 
viviparous. 


CHAPTER   XV 

SUBPHYLUM  VERTEBRATA:  CLASS  I.     CYCLOSTOMATA 

The  Cyclostomata  (Fig.  352)  are  vertebrates  that  have  a 
superficial  resemblance  to  eels,  but  differ  from  them  as  well  as 
from  all  other  vertebrates  in  many  important  respects.  They 
are  without  functional  jaws  and  lateral  appendages,  and  have 


Fig.  352.  —  Cyclostomes.  A,  Bdellostoma  dombeyi.  Light  apertures  along 
side  are  mucous  pits;  dark  apertures  are  branchial  openings.  B,  Myxine 
glutinosa.  Left  common  branchial  aperture  is  at  *.  C,  Petromyzon  marinus, 
(From  Dean.) 


only  one  olfactory  pit.  Cyclostomes  are  commonly  known  as 
hags  and  lampreys.  There  are  two  subclasses,  the  Myxinoidea 
or  hagfisljes,  and  the  Petromyzontia  or  lampreys;  the  former 
are  all  marine;  the  latter  are  found  both  in  salt  water  and  fresh 
water.  They  usually  feed  on  the  mucus,  blood,  and  even  the 
internal  organs  of  fishes,  which  they  attack  with  their  rasping 
mouth. 

414 


CLASS  CYCLOSTOjMATA 


415 


I.  The  Lamprey  —  Petromyzon 

Petromyzon  marinus,  the  sea  lamprey  (Fig.  352,  C),  inhabits 
the  waters  along  the  Atlantic  coast  of  North  America,  the  coasts 
of  Europe,  and  the  west  coast  of  Africa.  It  swims  about  near 
the  bottom  by  undulations  of  its  body,  or,  when  in  a  strong  cur- 
rent, progresses  by  darting  suddei^y  forward  and  attaching  itself 
to  a  rock  by  means  of  its  suctorial 
mouth.     In  the  spring  the   lamprey 


bucj- 


353 


Ventral    view 


ascends  the  rivers  to  spawn. 

External  Features.  —  The  lamprey 
reaches  a  length  of  about  three  feet. 
Its  body  is  nearly  cylindrical,  except 
at  the  posterior  end,  where  it  is 
laterally  compressed.  There  is  no 
exoskeleton.  The  skin  is  soft  and  is 
made  slimy  by  secretions  from  epi- 
dermal glands.  It  is  mottled  greenish 
brown  in  color.  A  row  of  segmental 
sense  pits,  the  lateral  line,  lies  on  each 
side  of  the  body  and  on  the  head. 
The  mouth  (Fig.  353,  mth)  Hes  at  the 

bottom  of  a  suctorial  disc,  the  buccal    °f  ^^^  ^^^  "f  Petromyzon  ma- 

'  rtnus.     buc.f,    buccal    funnel; 

funnel  (bucf),  and  is  held  open  by  a  mth,  mouth  ;  p,  papilla  ; 
ring  of  cartilage  (Fig.  354,  2).    Around   J;  ^;  '\}-^''}  ^/  ^^^^^^  ^"i?^^^' 

o  o     \      o   00-r^     /  14^   teeth    of    tongue.      (From 

the  mouth  are  a  number  of  papillce   Parker.) 
(Fig.  353,  p)  and  horny  teeth  {t^-f). 

Just  beneath  the  mouth  is  a  piston-like  tongue  which  also  bears 
teeth  (^).  On  each  side  of  the  head  is  an  eye,  and,  posterior 
to  the  eye,  seven  gill-slits  (Fig.  352,  C).  Between  the  eyes 
on  the  dorsal  surface  is  a  single  opening,  the  nasal  aperture 
(Fig.  355,  na").  The  anus  opens  on  the  ventral  surface  near 
the  posterior  end;  just  behind  it  is  the  urinogenital  aperture  in 
the  end  of  a  small  papilla.  There  are  two  dorsal  fins  and  one 
caudal  fin  (Fig.  352,  C). 


41 6  COLLEGE  ZOOLOGY 

The  Skeleton  (Fig.  354). — The  notochord  of  Petromyzon 
persists  as  a  well-developed  structure  in  the  adult  (Fig.  355,  nc\ 
Fig.  354,  12).  In  the  trunk  region  the  notochord  is  supple- 
mented by  small  cartilaginous  neural  arches  (Fig.  354,  jj). 
Cartilaginous  rays  hold  the  fins  upright.  The  organs  in  the  head 
are  supported  by  a  cartilaginous  skull  and  a  cartilaginous  bran- 
chial basket  (jo). 

The  skull  is  very  simple.  Its  principal  parts,  as  shown  in 
Figure  354,  are  an  annular  cartilage  (2)  which  holds  the  mouth 


Fig.  354.  —  Lateral  view  of  skull  of  Petromyzon  marinus.  i,  horny  teeth; 
2,  annular  cartilage;  3,  anterior  labial  cartilage;  4,  posterior  labial  cartilage; 
5,  nasal  capsule;  6,  auditory  capsule;  7,  dorsal  portion  of  trabeculjE;  S,  lateral 
distal  labial  cartilage;  9,  lingual  cartilage;  10,  branchial  basket;  //,  cartilag- 
inous cup  supporting  pericardium  ;  12,  sheath  of  notochord  ;  13,  anterior 
neural  arches  fused  together.     (From  Shipley  and  MacBride,  after  Parker.) 

open,  two  labial  cartilages  (j,  4)  which  form  a  roof-like  support 
for  the  buccal  funnel,  a  lingual  cartilage  (g)  supporting  the 
tongue,  an  olfactory  capsule  (5),  two  auditory  capsules  (6),  and 
a  cranial  roof  (7).  The  branchial  basket  is  a  cartilaginous  frame- 
work (10)  which  supports  the  gill-sacs  and  the  walls  of  the  peri- 
cardium (ti). 

The  Muscular  System.  —  The  muscles  of  the  body- wall  are 
zigzag  myotomes  (Fig.  355,  d.m,  v.m.).  The  tongue  {t,  t^) 
is  moved  by  large  muscles  {p.m.t,  r.pt.t.),  and  the  buccal  funnel 
is  supplied  with  a  number  of  radiating  muscles. 

The  Digestive  System.  —  Pg^qmyson  lives  on  the  blood  _gf 
other  animals.  The  expansion  of  the  buccal  funnel  (Fig.  355, 
o.f.)  causes  the  mouth  to  act  like  a  sucker  and  enables  the  ani- 
mal to  cling  to  stones  or  to  fasten  itself  to  fishes  such  as  shad, 


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41 8  COLLEGE   ZOOLOGY 

sturgeon,  cod,  and  mackerel.  With  its  rasp-like  tongue  a 
hole  is  made  in  the  flesh  of  the  victim  and  the  blood  sucked 
out. 

The  mouth  opens  into  a  buccal  cavity  (Fig.  355,  m).  Two 
tubes  lead  posteriorly  from  the  latter,  a  dorsal  (esophagus  (oss) 
and  a  ventral  respiratory  tube  (r.t),  guarded  by  a  fold  called  the 
velum  (vl).  There  is  no  distinct  stomach.  The  oesophagus  is 
separated  from  the  intestine  (int)  only  by  a  valve.  A  fold  in  the 
intestine  called  the  typhlosole  (see  also  p.  219)  forms  a  sort  of 
spiral  valve.  A  liver  (Ir)  is  present,  but  there  is  usually  no  bile 
duct  (b.d.)  in  the  adult. 

The  Circulatory  System.  —  Petromyzon  possesses  a  heart, 
a  number  of  veins  and  arteries,  and  many  lymphatic  sinuses 
(Fig.  355,  ^,  s').  The  heart  lies  in  the  pericardium  (pc),  and 
consists  of  a  ventricle  (v)  which  forces  the  blood  into  the  arteries 
and  an  auricle  (au)  which  receives  the  blood  from  the  veins.  A 
renal  portal  system  is  absent. 

The  Respiratory  System.  —  Respiration  is  carried  on  by  means 
of  seven  pairs  of  gill  pouches  (Fig.  355,  br.^),  which  open  to  the 
outside  by  the  gill-slits  (e.a)  and  internally  to  the  respiratory 
tube  (r.t).  Each  gill  pouch  contains  numerous  gill  lamellce 
(br.^).  Water  is  taken  into  the  gill-sacs  through  the  gill-slits, 
and  discharged  by  the  same  openings. 

The  Nervous  System.  —  The  brain  (Fig.  355,  br.)  of  the  adult 
lamprey  is  very  primitive  and  in  many  respects  similar  to  that 
of  the  embryos  of  higher  vertebrates.  It  is  remarkable  because 
of  its  thin  membranous  roof  and  the  small  band-like  cerebellum. 
The  spinal  cord  is  flat,  and  lies  on  the  floor  of  the  neural  canal 
(n.ca.).. 

The  Sensory  Organs.  —  Organs  of  taste,  smelly  hearingj^nd 
sight  are  present  in  the  lamprev.  The  end  organs  of  taste  are 
situated  between  the  gill  pouches  on  the  pharyngeal  wall.  The 
organ  of  smell  is  an  olfactory  sac  (Fig.  355,  na)  which  lies  in  the 
nasal  capsule  (Fig.  354,  5)  and  opens  by  a  nasal  aperture  (Fig. 
355)  ^^'0  on  the  dorsal  surface  between  the  eyes.     The  olfactory 


CLASS   CYCLOSTOMATA  41 9 

sac  gives  off  ventrally  a  tube  of  unknown  function,  called  the 
hypophysis  or  pituitary  body  (Fig.  355,  na'). 

The  auditory  organs  of  Fetromyzon,  which  lie  in  the  auditory 
capsule  (Fig.  354,  6),  have  only  two  semicircular  canals  instead 
of  the  usual  number,  three  (Fig.  350).  The  hagfish  has  only 
one.     The  eyes  of^  the  lamprey  aye  poorly  developed. 

The  Urinogenital  System.  —  The  excretory  and  reproductive 
systems  are  so  closely  united  in  the  lamprey  that  it  is  custo- 
mary to  treat  them  together  as  the  urinogenital  system.  The 
kidneys  He  along  the  dorsal  wall  of  the  body-cavity,  and  each 
pours  its  secretions  by  means  of  a  duct,  called  the  ureter,  into 
the  urinogenital  sinus,  and  thence  to  the  outside  through  the 
urinogenital  aperture.  The  sexes  are  separate^but  eggs  are  sonie- 
times  present  in  the  testis  of  the  male.  The  single  gonad  (Fig. 
355,  ov)  fills  most  of  the  abdominal  cavity.  The  germ-cells 
break  out  into  the  coelom,  make  their  way  through  two  genital 
pores  into  the  urinogenital  sinus,  and  then  pass  out  through  the 
urinogenital  aperture  into  the  water,  where  fertilization  occurs. 

Development.  —  The  eggs  produce  larvae  known  as  Ammo- 
coetes.  The  larva  differs  in  many  respects  from  the  adult,  and 
apparently  represents  a  stage  of  development  intermediate 
between  Amphioxus  and  a  primitive  vertebrate.  As  in  Amphi- 
oxus,  food  particles  are  drawn  into  the  mouth  by  means  of  a 
current  of  water  produced  by  cilia.  An  endostyle,  which  repre- 
sents the  thyroid  gland  of  the  adult,  secretes  mucus  which  en- 
tangles the  food  and  carries  it  into  the  alimentary  canal. 

The  Ammocoetes  lies  buried  in  mud  and  sand,  and  probably 
keeps  its  skin  free  from  bacteria,  fungi,  and  other  parasitic 
growths  by  means  of  an  integumentary  secretion.  In  the  winter 
of  the  third  or  fourth  year  the  larval  lamprev  undergoes  a  meta- 
morphosis during  which  the  structure  and  habits  of  the  adult 
are  acquired. 

Relationships.  —  The  hagfishes  and  lampreys  are  the  lowest 
vertebrates.  Many  of  their  structures,  such  as  the  cranium 
and  vertebral  column,  are  very  primitive,  but  others  are  appar- 


420  COLLEGE  ZOOLOGY 

ently  highly  specialized.     The  absence  of  jaws  and  of  limbs 
may  be  due  to  degeneration. 

Economic  Importance.  —  The  flesh  of  the  lamprey  is  used  as 
food  both  in  Europe  and  America.  The  number  of  lampreys, 
however,  has  decreased  so  much  within  recent  years  that  their 
value  as  food  is  now  almost  negligible.  Fishermen  charge  the 
lamprey  with  destroying  numbers  of  food  fishes,  which  are 
attacked  just  beneath  the  pectoral  fins.  The  flesh  is  torn  with 
their  rasping  teeth  and  the  blood  sucked  out  of  the  body. 

2.   Cyclostomata  in  General 

Subclass  I.  Myxinoidea. — The  Hagfishes. — One  family, 
the  Myxinid^,  belongs  to  this  subclass.  The  Myxinid^  are 
all  marine,  and  are  represented  by  three  genera:  (i)  Bdellostoma 
(Fig.  352,  A)  and  (2)  Paramyxine  in  the  Pacific,  and  (3)  Myxine 
(Fig.  352,  B)  in  the  Pacific,  Atlantic,  and  North  Sea.  These 
hagfishes  differ  from  the  lampreys  in  a  number  of  characters: 
(i)  the  nasal  aperture  is  terminal;  (2)  the  pituitary  body  opens 
into  the  pharynx;  (3)  there  are  four  tentacles  on  either  side  of  the 
mouth;  (4)  the  oral  sucker  is  absent,  and  there  is  only  a  single, 
large  tooth;  (5)  there  are  no  neural  arches  in  the  trunk,  and  the 
branchial  basket  is  poorly  developed ;  and  (6)  the  gills  may  open 
by  a  single  common  pore  on  each  side  (Myxine). 

The  hagfishes  Hve  in  the  mud  of  the  sea  bottom  down  to  a 
depth  of  nearly  three  hundred  and  fifty  fathoms.  They  are 
very  destructive  to  fishes,  especially  those  caught  on  lines  or  in 
nets,  boring  their  way  into  the  body  and  eating  out  the  soft 
parts.     Cod  and  flounders  are  the  fish  usually  attacked. 

Subclass  II.  Petromyzontia.  —  The  Lampreys.  —  The 
lampreys  all  resemble  Petromyzon  in  general  structure.  There 
is  a  single  family,  Petromyzontid^,  and  a  number  of  genera. 
Petromyzon  inhabits  the  rivers  and  seas  of  America,  Europe, 
and  Asia;  Lampetra  and  Ichthyomyzon  live  in  North  American 
streams  and  lakes;  Mordacia  and  Geotria  in  South  America 
and  Tasmania. 


CLASS   CYCLOSTOMATA 


421 


Lampetra  wilderi,  the  brook  lamprey  of  North  America,  breeds 
in  the  spring.  Stones  are  moved  by  means  of  the  buccal  funnel 
until  a  space  is  cleared  on  the  bottom  where  a  number  of 
individuals  congregate  (Fig.  356).  A 
male  clings  to  the  head  of  a  female  for 
a  moment,  winds  his  tail  about  >  her 
body,  and  discharges  spermatozoa  over 
the  eggs  when  they  are  extruded.  The 
adults  die  soon  after  spawning;  they 
probably  take  no  food,  and  are  there- 
fore not  injurious  to  fishes. 


Fig.  356.  — Lampetra  wilderi,  in  the 
act  of  spawning.  (From  Shipley  and 
MacBride,  after  Dean  and  Sumner.) 


Fig.  357.  —  PalcBospon- 
dylus  gunni,  a  Devonian 
Cyclostome.  (From  Dean, 
after  Traquair.) 


A  fossil  vertebrate,  Palceospondylus  gunni  (Fig.  357),  was 
probably  closely  allied  to  the  cyclostomes.  It  was  found  in 
the  Devonian  rocks  of  Scotland  and  is  about  an  inch  long. 


CHAPTER    XVI 

SUBPHYLUM    VERTEBRATA:     CLASS    H.     ELASMO- 
BRANCHII 

The  elasmobranchs  are  the  sharks,  dogfish  sharks,  and  rays 
or  skates.  They  resemble  the  true  fishes  (Pisces,  Chapter 
XVII)  in  external  form,  but  differ  from  them  so  widely  in  struc- 
ture that  they  are  placed  in  a  class  by  themselves.^  The 
elasmobranchs  exhibit  a  number  of  structural  advances  over 
the  cyclostomes;  there  are  paired  fins,  a  lower  jaw,  gill  arches, 
and  placoid  scales.  Among  the  peculiarities  which  separate 
the  elasmobranchs  from  the  true  fishes  (Pisces)  are  the  absence 
of  membrane  bones,  of  an  air  bladder,  and  of  true  scales,  and 
the  presence  of  skeletal  characteristics  which  are  not  found  in 
true  fishes.  Two  subclasses  of  living  elasmobranchs  are  recog- 
nized: the  Selachh  or  sharks  and  rays,  and  the  Holocephali 
or  chimaeras. 

I.  The  Dogfish  Shark  —  Squalus  acanthias 

The  common  dogfish  shark  (Fig.  358)  is  abundant  in  the 
waters  off  the  coast  of  New  England  and   northern  Europe. 


Fig.  358.  —  The  dogfish  shark,  Squalus  acanthias.     (From  Dean,  after  Goode.) 

^  See  Jordan,  Guide  to  the  Study  of  Fishes,  Vol.  I.  pp.  506-511. 
422 


CLASS  ELASMOBRANCHII 


423 


424  COLLEGE  ZOOLOGY 

It  is  widely  used  for  laboratory  study,  and  detailed  accounts  of 
its  anatomy  may  be  found  in  several  laboratory  manuals.  It 
will  suffice  here  to  point  out  certain  of  its  more  prominent 
characteristics. 

External  Features.^  —  The  body  is  fusiform  and  about  two 
and  one  half  feet  long.  There  are  two  dorsal  fins  (Fig.  359,  D) 
each  with  a  spine  (not  shown  in  Fig.  359)  at  the  anterior  end,  two 
pectoral  fins,  and  two  ventral  fins  (VF).  The  ventral  fins  in  the 
male  possess  cartilaginous  appendages,  known  as  claspers  (CV). 
The  tail  is  heterocercal  (see  Chap.  XVII).  The  mouth  is  a  trans- 
verse slit  on  the  ventral  surface  of  the  head.  On  either  side  above 
the  mouth  is  an  eye,  and  in  front  an  olfactory 
organ  (Fig.  359,  N).  Anterior  to  each 
pectoral  fin  are  six  gill-slits  (GS),  the  first 
of  which  is  situated  just  back  of  the  eye 
scak''of°'G"re^eLTand  ^^^  modified  as  a  spiracle  (SF).  Between 
shark  viewed  from  the  ventral  fins  is  the  cloacal  opening  (CL). 
itnf  '""•  ^^'""^  The  surface  is  covered  with  i>la<:oid  scales 
or  dermal  denticles  (Fig.  360)  which  form 
shagreen.  They  represent  a,  primitive  exoskeletal  structure 
and  have  been  the  starting-point  for  the  development  of  the 
scales  and  bony  plates  of  the  true  fishes. 

Over  the  jaws  they  are  modified  as  teeth  with  their  points 
directed  backward,  and  are  used  for  holding  and  tearing  prey. 
A  placoid  scale  consists  of  a  bony  basal  plate  with  a  spine  in  the 
center  composed  of  dentine  and  covered  with  enamel. 

The  Skeleton.  —  The  skeleton  is  cartilaginous.  The  axial 
skeleton  consists  of  the  vertebral  column,  skull,  and  visceral 
arches.  The  vertebrce  (Fig.  359,  C)  are  hour-glass-shaped 
(amphicoelous),  and  the  notochord  persists  in  the  lenticular  spaces 
between  them.  The  skull  is  much  more  highly  developed  than 
that  of  the  cyclostomes.  It  is  composed  principally  of  the 
cranium  or  brain  case  (CC),  two  large  anterior  nasal  capsules, 

1  Figure  359  shows  the  anatomy  of  a  shark  which  differs  slightly  from  that  of  the 
dogfish  shark. 


CLASS   ELASMOBRANCHII  425 

and  two  posterior  auditory  capsules.  The  visceral  skeleton^  com- 
prises  the  jaws,  the  hyoid  arch,  and  five  branchial  arches.  The 
q^endicular  skeleton  consists  of  the  skeletons  of  the  fins  {B,  R) 
and  those  of  the  pectoral  and  pelvic  girdles  which  support  them. 

The  Digestive  System.  — The  alimentary  canal  is  longer  than 
the  body.  Following  the  mouth  (Fig.  359,  M)  is  a  large  pharynx 
into  which  open  the  spiracles  and  gill-clefts.  The  pharynx  leads 
into  the  short,  wide  oesophagus  which  opens  into  the  U-shaped 
stomach  (S).  The  hinder  end  of  the  stomach  is  provided  with 
a  sphincter,  or  circular  muscle  marking  it  off  from  the  intestine. 
The  latter  is  provided  interiorly  with  a  spiral  fold  of  mucous 
membrane,  called  the  spiral  valve  (I),  which  furnishes  a  large 
surface  for  absorption  and  prevents  the  too  rapid'  passage  of 
food.  The  liver  (L)  is  large,  and  consists  of  two  long  lobes;  its 
secretion,  the  bile,  is  stored  up  in  a  ^all-bladder  and  emptied 
through  the  bile-duct  into  the  intestine.  A  panQr^a^  and  spleen 
are  also  present. 

The  Circulatory  System  (Fig.  361). — As  in  the  cyclostomes 
and  most  of  the  true  fishes,  the  heart  (Fig.  361,  s.v,  au,  v,  cart) 
contains  venous  blood  only.  This  is  pumped  through  the 
ventral  aorta  (v.ao)  and  thence  into  the  aferent  branchial  arteries 
(a.br.a),  becoming  oxygenated  in  the  capillaries  of  the  gills. 
It  then  passes  into  the  eferent  branchial  arteries  (e.br.a),  which 
carry  it  to  the  dorsal  aorta  (d.ao).  The  dorsal  aorta  supplies 
the  various  parts  of  the  body  as  shown  in  Figure  361.  Veins 
carry  the  blood  back  to  the  heart,  opening  into  the  sinus  venosus 
(s.v).  Other  veins,  called  the  hepatic  i^ortal  system  (h.i).v), 
transport  the  blood  from  the  alimentary  canal,  pancreas,  and 
spleen  to  the  liver.  A  third  system,  the  renal  portal  system 
(r.p.v),  conveys  the  blood  from  the  hinder  portion  of  the  body 
to  the  kidneys. 

The  Respiratory  System.  —  Respiration  is  carried  on  by  means 
of  ^ills.  These  are  folds  of  mucous  membrane  well  supplied 
with  blood-vessels  and  borne  by  the  hyoid  arch  and  first  four 
branchial  arches.     They  are  supported  both  by  these  arches  and 


o  S  S  "^  S  " 
2  rt  _^  <u  «  a 
a"  ^  t^  c   c   > 


CLASS  ELASMOBRANCHII 


427 


by  gill-rays.     Water  entering   the   mouth  passes  between  the 
branchial  arches  and  out  through   the  gill-slits  (Fig.  359,  GS). 
thus  bathing  the  gills  and  supply- 
ing  oxygen  to  the  branchial  blood- 
vessels. 

The  Nervous  System.  —  The  ^ 
brain  (Fig.  362)  is  more  highly 
developed  than  that  of  the  cyclo- 
stomes.  It  possesses  two  remark- 
ably large  olfactory  lobes  (j),  a 
cerebrum  of  two  hemispheres  (4), 
a  pair  of  optic  lobes  (7),  and  a 
cerebellum  {g)  which  projects 
backward  over  the  medulla  oblon- 
gata (lo).  There  are  ten  pairs  of 
cranial  nerves  (Fig.  362  and  Table 
XIV).  The  spinal  cord  is  a  dorso- 
ventrally  flattened  tube  with  a 
narrow  central  canal;  it  is  pro- 
tected by  the  vertebral  column. 
Spinal  nerves  arise  from  its  sides 

^  *  Fig.  362.  —  Brain  of   a    dogfish 

The  Sense-organs.  —  The  olfac-    shark,     ScylUum     catulus,     dorsal 

tory  sac  (Fig.  362)  is  characteristi-    ^'r^-     ^'  pineal  stalk;  5,  olfactory 
■^  \     o    o      /  \q\jq  .       ^^     cerebral    hemisphere  ; 

cally  large  in  elasmobranchs.     The    5,    thalamencephalon ;     7,    optic 

ears    (Fig.    350)    are    membranous    lobes;    9.  cerebellum;    /o,  roof  of 

^     ^     OD   y  ^   ^  hind-brain;  //,  12,  13,  14,  muscles 

sacs  each  with   three   semicircular    that  move  the  eyeball;    15,  ninth 

canals;  they  lie  within  the  auditory    ^^^^^'  '^'  '^''\  b^-fn^he^  «/  ^^g^s 

'  -^  ^  •'     nerve;    17,  main   trunk    of    vagus 

capsules.      The  eye^  (Fig.  362)    are    nerve;     II-X,  roots  of  the  cranial 

well  developed.  Along  each  side 
of  the  head  and  body  is  a  longi- 
tudinal groove,  called  the  lateral  line  (Fig.  359,  LV),  and  on 
the  head  are  also  mucous  canals  which  open  on  the  dorsal  and 
ventral  surfaces  and  end  in  ampullae  at  the  anterior  end  of  the 
snout.     These  structures  are  supposed  to  be  sensory  in  function. 


nerves. 
Bride.) 


(From  Shipley  and  Mac- 


428  COLLEGE  ZOOLOGY 

The  Urinogenital  System.  —  The  dogfish  shark  possesses  two 
ribbcn-like  kidneys  (Fig.  359,  K),  one  on  either  side  of  the  dorsal 
aorta.  Their  secretion  is  carried  by  small  ducts  into  a  larger 
duct,  the  ureter  (UD),  which  empties  into  a  urinogenital  sinus; 
it  then  passes  out  of  the  body  through  the  cloacal  aperture  (CL). 
A  series  of  yellowish  gland-like  bodies,  called  suprarenals,  are 
associated  with  the  kidneys. 

The  spermatozoa  of  the  male  arise  in  two  testes  and  are  car- 
ried by  the  vasa  deferentia  into  the  urinogenital  sinus.  During 
copulation  they  are  transferred  to  the  oviducts  of  the  female 
with  the  aid  of  the  claspers. 

The  eggs  of  the  female  arise  in  the  single  ovary  (Fig.  359,  OF), 
which  is  attached  to  the  dorsal  wall  of  the  abdominal  cavity. 
They  break  out  into  this  cavity  and  enter  the  funnel-like  open- 
ings of  the  oviducts  {OVD).  When  they  reach  an  expanded 
portion,  called  the  oviducal  gland,  they  receive  a  horny  covering 
which  protects  them  from  injury  after  they  are  laid. 

2.   Elasmobranchs  in  General 

The  chief  characteristics  of  the  elasmobranchs  are  the  presence 
of  a  cartilaginous  skeleton,  a  persistent  notochord,  placoid  scales, 
a  spiral  valve  in  the  intestine,  and  claspers  in  the  male;  and  the 
absence  of  a  gill-cover  or  operculum,  pyloric  ca^ca,  and  an  air- 
bladder.  The  mouth  is  a  transverse  aperture  on  the  ventral 
side  of  the  head. 

Subclass  I.  Selachii.  —  There  are  two  distinct  types  of 
elasmobranchs  belonging  to  this  subclass:  (i)  sharks,  which  are 
slender  and  cylindrical  and  have  the  gill-slits  on  the  side;  and 
(2)  rays,  which  are  flattened  dorso-ventrally  and  have  the  gill- 
slits  underneath. 

Order  i.  Squall.  —  Sharks  and  Dogfish  Sharks. — The 
sharks  and  dogfish  sharks  resemble  in  general  the  common  horned 
dogfish  shark  (Fig.  358).  Most  sharks  are  under  eight  feet  in 
length,  and  although  carnivorous  and  voracious,  very  seldom 
attack  man.     They  feed  principally  on  small  fish,  squids,  and 


CLASS  ELASMOBIL\NCHII 


429 


Crustacea.  The  great  white  shark,  Carcharodon  carcharias, 
occurs  in  all  warm  seas.  It  reaches  a  length  of  over  thirty  feet 
and  has  earned  the  name  of  man-eater  by  occasionally  devouring 
a  human  being.     One  of  the  most  peculiar  sharks  is  the  hammer- 


FiG.  363. — Hammerhead  shark,  Sphyrna  tudes.     af.,  anal  fin;  c.f,  caudal 
fin;  cl,  clasper;  e,  eye.     (From  Lankester's  Treatise,  after  Day.) 

head,  Sphyrna  tildes  (Fig.  363),  which  is  also  found  in  warm  seas. 
Its  head  is  shaped  like  the  head  of  a  mallet,  with  an  eye  {e)  at 
either  end. 

Order  2.     Raji.  —  Rays  or  Skates.  —  The  rays  or  skates  are 
flattened  dorso-ventrally  and  adapted  for  living  on  the  bottom. 


Fig.  364.  —  Sawfish,  Pristis  pectinatus.     A,  side  view.     B,  ventral  view. 
(From  Dean;  A,  after  Goode.) 


Some  of  them  are  only  slightly  flattened,  whereas  others  are 
broader  than  long.  The  sawfish,  Pristis  pectinatus  (Fig.  364), 
lives  in  tropical  seas  and  is  abundant  in  the  Gulf  of  Mexico. 
It  reaches  a  length  of  from  ten  to  twenty  feet.  The  saw  of 
a  large  specimen  is  about   five   feet   long;    it   is   used   as   a 


430 


COLLEGE  ZOOLOGY 


Fig.  365. 


Sting-ray,  Dasyatis  sabina,  dorsal  view. 
Evermann.) 


(From  Jordan  and 


weapon  of  defense,  and  dangerous  sidewise  strokes  can  be  made 

with  it. 

The  sting-ray,  Dasyatis  sabina  (Fig.  365),  lives  half  buried  in  the 

sand  along  the  coast  of  Florida. 
There  is  a  barbed  spine  on  its  whip- 
like tail  which  makes  a  painful 
wound  if  driven  into  the  hand  or 
naked  foot.  The  torpedo  (Family 
ToRPEDiNiDyE,  Fig.  366)  is  inter- 
esting because  of  the  presence  of 
modified  bundles  of  muscles  (Fig. 
366,  EO)  lying  on  either  side  of  the 
head  which  are  capable  of  storing 
up  electrical  energy  and  discharg- 
ing it.  The  discharge  of  these  elec- 
tric organs  is  sufficient  to  paralyze 
large  animals;  they  thus  may  serve 
as  weapons  of  offense  and  defense. 

Fig.  366.  —  Torpedo  with  electric  organ,  EO,  and  brain  exposed,  dorsal 
view,  Br,  branchial  sacs;  GR,  sensory  canal  tubes  of  the  skin;  Le,  electric 
lobe  of  brain;  O,  eye-;  Tr,  trigeminal  nerve;  V,  vagus  nerve.  (From  Sedg- 
wick's Zoology,  after  Gegenbaur.) 


CLASS   ELASMOBRANCHII 


431 


Subclass  II.  Holocephali.  —  The  members  of  this  subclass 
differ  from  the  Selachii  in  a  number  of  minor  structural  char- 
acters.    There  is  a  single  family,  the  CHiM^ERiDiE,  containing 


367.  —  ChinKBra  monslrosa,  male,     m,  mouth;  n.p,  frontal  clasper: 
op,  operculum.     (From  the  Cambridge  Natural  History.) 


three  genera.     The  species  shown  in  Figure  367  is  the  sea-cat 
of  the  North  Atlantic. 


3.   The  Economic  Importance  of  Elasmobranchs 

Many  destructive  species  belong  to  the  elasmobranchs.  The 
smooth  dogfish  shark,  Mustelus  cams,  is  an  important  enemy  of 
the  lobster.  It  is  estimated  that  the  minimum  number  of  lob- 
sters destroyed  by  these  dogfish  sharks  in  Buzzards  Bay  during 
one  year  is  about  640,000.  The  sand-shark,  Carcharias  littoralis, 
devours  large  numbers  of  valuable  fishes,  including  menhaden, 
flounders,  and  scup.  The  horned  dogfish  shark,  Squalus  acan- 
thias  (Fig.  358),  is  the  most  serious  destructive  agency  with  which 
fishermen  have  to  contend.  It  devours  valuable  food  fishes, 
drives  away  or  destroys  schools  of  squid  used  by  the  fishermen 
for  bait,  and  robs  and  injures  nets  and  other  fishing  gear.  Experts 
estimate  the  damage  from  dogfish  sharks  to  marketable  fish  and 
fishing  gear  owned  in  Massachusetts  at  not  less  than  $400,000 
per  year.  They  suggest  that  dogfish  sharks  be  converted  into 
oil  and  fertilizer  so  as  to  make  it  profitable  for  fishermen  to 
capture  them  and  thus  bring  about  a  decrease  in  their  numbers. 


CHAPTER    XVII 


SUBPHYLUM    VERTEBRATA:    CLASS    III.     PISCES 


The  Pisces  are  the  true  fishes.  The  class  includes  the  com- 
mon fishes  and  the  lung-fishes.  They  are  aquatic  animals  and 
are,  therefore,  adapted  to  life  in  the  water.  The  respiratory 
organs  of  fishes  are  ^ills.  Usually  a  dermal  exoskeleton  of  scales 
or  bony  plates  furnishes  a  protective  covering  for  the  body. 
Living  fishes  are  grouped  into  two  subclasses. 

Subclass  I.  Teleostomi.  —  Fishes  with  a  skeleton  consist- 
ing wholly  or  partially  of  bone,  usually  with  scales  (never  placoid 
scales),  and  a  well-developed  operculum  covering  the  gills. 

Subclass  II.  Dipnoi.  —  Fishes  with  a  skeleton  of  cartilage 
and  bone,  a  single  or  double  lung,  and  an  operculum  covering 
the  gills. 

I.   A  Bony  Fish  —  The  Perch 

External  Features.  —  The  yellow  perch,  Perca  flavescens  (Fig. 
368),  inhabits  the  fresh- water  streams  and  lakes  of  the  north- 


FiG.  368.  —  Perch,  Perca  flavescens. 
432 


(From  Dean,  after  Goode.) 


CLASS  PISCES 


433 


eastern  United  States,  and  ranges  west  to  the  Mississippi  Valley. 
Its  body  is  about  a  foot  long  and  is  divisible  into  head,  trunk,  and 
tail.  There  are  two  dorsal  fins,  a  caudal  fin,  a  single  median  anal 
fin  just  posterior  to  the  anus,  two  lateral  ventral  fins,  and  two 
lateral  pectoral  fins.  On  each  side  of  the  body  is  a  lateral  line. 
The  head  bears  a  mouth  with  well-developed  jaws  armed  with 
teeth,  a  pair  of  lateral  eyes,  a  pair  of  nasal  apertures  in  front  of 
each  eye,  and  gill-covers  or  opercula  beneath  which  are  the  gills. 
The  skin  is  provided  with  a  number  of  dermal  scales  which  are 
arranged  like'  the  shingles  on  the  roof  of  a 
house,  and  protect  the  fish  from  mechanical 
injury. 

Locomotor  Organs.  —  The  body  of  the 
perch,  and  of  most  other  fishes,  is  spindle- 
shaped  and  offers  little  resistance  to  the 
water  through  which  the  animal  swims 
(Fig.  369).  It  is  kept  at  the  same  weight 
as  the  amount  of  water  it  displaces  by 
means  of  an  air-bladder.  The  fish  is  thus 
able  to  remain  stationary  without  muscular 
exertion.  The  principal  locomotor  organ  is 
the  tail.  By  alternating  contractions  of 
the  muscular  bands  on  the  sides  of  the 
trunk  and  tail,  the  tail  with  its  caudal  fin  is 
lashed  from  one  side  to  the  other,  moving  in  a  curve  shaped  like 
a  figure  8  as  shown  in  Figure  370.  Similar  movements  are  em- 
ployed in  sculling  a  boat,  and  the  method  of  progress  is  analogous 
to  the  action  of  the  screw  of  a  steamer.  During  the  flexions 
and  extensions  of  the  tail,  the  trunk  is  curved  in  such  a  way  as 
to  bring  about  the  most  effective  extension  or  forward  stroke 
and  a  weak  flexion  or  non-effective  stroke. 

The  fins  are  integumentary  expansions  supported  by  bony  or 
cartilaginous  rays.     The  paired  lateral  fins  (pectoral  and  ven- 
tral) are  used  as  oars  in  swimming,  but  only  when  the  fish  is 
moving  slowly.     They  also  aid  the  caudal  fin  in  steering  the 
2  F 


Fig.  369.  —  Front 
view  of  a  fish  (Spanish 
mackerel).  (From 
Dean.) 


434 


COLLEGE  ZOOLOGY] 


animal,  for,  although  the  course  is  altered  largely  by  the  pointing 
of  the  head  and  tail  in  the  desired  direction,  the  lateral  fins  assist 
in  swerving  the  body  to  one  side  or  the  other,  either  by  executing 
more  powerful  strokes  on  one  side,  or  by  the  expansion  of  one 
fin  and  the  folding  back  of  the  other.  These  methods  are  like 
those  used  in  steering  a  rowboat  with 
oars.  Movement  up  or  down  results 
from  holding  the  lateral  fins  in  certain 
positions  —  obliquely  backwards  with  the 
anterior  edge  higher  for  the  ascent,  and 
obliquely  forwards  for  the  descent. 

Fishes  must  maintain  their  equilibrium 
in  some  way,  since  the  back  is  the  heaviest 
part  of  the  body  and  tends  to  turn  them 
over.  The  dorsal,  anal,  and  caudal  fins 
increase  the  vertical  surface  of  the  body 
(Fig.  369)  and,  like  the  keel  of  a  boat, 
assist  the  animal  in  maintaining  an  upright 
position.  The  paired  lateral  fins  are  also 
organs  of  equilibration,  acting  as  balancers; 
if  both  pectoral  fins  are  removed,  the  an- 
terior end  of  the  fish  sinks  downward;  if  a 
pectoral  or  both  pectoral  and  ventral  fins 
are  removed  from  one  side,  the  fish  turns 
toward  that  side;  and  if  all  four  lateral 
fins  are  cut  off,  the  fish  turns  completely 
over  with  the  ventral  surface  upward. 

The  Skeleton.  —  The  exoskeleton  of  the 
perch  includes  scales  and  fin-rays.  The 
scales  develop  in  pouches  in  the  dermis.  They  are  arranged 
in  oblique  rows  and  overlap  like  the  shingles  on  the  roof  of  a 
house,  thus  forming  an  efficient  protective  covering.  The 
posterior  edge  of  each  scale  which  extends  out  from  under  the 
preceding  scale  is  toothed,  and  therefore  rough  to  the  touch. 
Scales  of  this  kind  are  called  ctenoid  scales  (Fig.  371,  A).    The 


Fig.  370.  —  Diagram 
to  illustrate  the  mode  in 
which  the  tail  of  an  or- 
dinary fish  is  used  in 
swimming.  (From  the 
Cambridge  Natural  His- 
tory, after  Pettigrew.) 


CLASS  PISCES  435 

fin-rays  support  the  fins.  Those  of  the  first  dorsal  fin 
(Fig.  372,  Ri.),  and  at  the  anterior  edge  of  the  anal  {A) 
and  ventral  fins  (5),  are  unjoin  ted  and  unbranched  spines.  The 
caudal  {S)  and  pectoral  fins  {Br)  and  most  of  the  anal  and  ven- 
tral fins  are  supplied  with  jointed,  and  usually  branched,  soft 
fin-rays.  > 

The  endoskeleton  TFig.  372)  consists  principally  of  bones,  and 
includes  the  skull,  vertebral  column,  ribs,  pectoral  girdle,  and 


Fig.  371.  —  Scales.  A,  ctenoid.  B,  ganoid.  C,  cycloid.  (From  the 
Cambridge  Natural  History;  A,  B,  after  GUnther;  C,  after  Parker  and 
Haswell.) 

the  interspinal  bones  or  pterygiophores  {Fr)  which  aid  in  sup- 
porting the  unpaired  fins.  The  body  of  the  fish  is  to  a  consid- 
erable extent  supported  by  the  surrounding  water;  consequently, 
the  bones  do  not  need  to  be  so  strong  as  those  of  land  animals, 
like  birds  and  mammals,  which  must  support  the  entire  weight 
of  the  body. 

The  vertebrcB  (Fig.  372,  w)  are  simple  and  comparatively  uni- 
form in  structure.  They  are  called  amphicoelous  vertebrae 
because  the  centrum  has  concave  anterior  and  posterior  faces. 
A  typical  vertebra  has  a  cylindrical  supporting  centrum,  a  neural 
arch  through  which  the  spinal  cord  extends,  a  neural  spine  (oD) 
for  the  attachment  of  muscles,  and  short  ventral  projections,  the 
parapophyses,  to  which  the  ribs  are  attached.  The  centrum 
of  one  vertebra  is  connected  with  those  of  the  preceding  and 
following  vertebrae  by  ligaments.  The  spaces  between  the  centra 
contain  the  remains  of  the  notochord. 


436 


COLLEGE  ZOOLOGY 


Ribs  (Fig.  372,  R)  are  attached  by  ligaments  to  the  centra 
or  parapophyses  of  the  abdominal  vertebrae  and  serve  as  a  pro- 
tecting framework  for  the  body-cavity  and  its  contents.  There 
is  no  sternum.  Intermuscular  bones  (G)  are  also  attached  to 
some  of  the  vertebrae.  In  the  caudal  region  hcemal  arches  and 
hcemal  spines  (uD)  extend  down  from  the  centrum,  and  the 
caudal  artery  and  caudal  vein  pass  through  these  arches.     The 


Fig.  372.  —  Skeleton  of  perch.  A.,  anal  fin;  Au.,  orbit;  B.,  ventral  fin; 
Be,  pelvic  bones;  Br,  pectoral  fin;  Fr,  interspinous  bones;  Kd,  parts  of 
operculum;  0,  maxilla;  oD,  neural  spines;  R,  ribs;  Ri.,  ist  dorsal  fin; 
R2.,  second  dorsal  fin;  S,  caudal  fin;  Sch,  bones  of  shoulder  girdle;  u,  man- 
dible; uD,  haemal  spines;  z,  premaxilla.     (From  Schmeil.) 


extreme  posterior  portion  of  the  vertebral  column  is  modified 
so  as  to  furnish  a  support  for  the  caudal  fin  (S). 

The  skull  of  the  perch  (Fig.  372)  consists  of  a  large  number 
of  parts,  some  of  bone,  others  of  cartilage.  As  in  Petromyzon^ 
these  parts  may  be  grouped  into  the  cranium  and  the  visceral 
skeleton.  The  cranium  is  originally  of  cartilage,  but  becomes 
strengthened  by  the  addition  of  membrane  bones,  which  are 
dermal  ossifications.  The  cranium  protects  and  supports  the 
brain,  auditory  organs,  and  olfactory  sacs,  and  furnishes  orbits 
{Au)  for  the  eyes. 


CLASS  PISCES  437 

The  visceral  skeleton,  which  is  represented  in  Petromyzon  by 
the  branchial  basket  (Fig.  354,  10),  is,  in  the  perch,  composed  of 
seven  arches  more  or  less  modified.  The  first  or  mandibulctr 
arch,  forms  the  jaws.  The  upper  jaw  consists  principally  of  two 
.pairs  of  bones,  the  premaxillcB  (Fig.  372,  z)  and  the  maxillcB  (0). 
The  premaxillae  bear  teeth.  The  lower  jaw  or  mandible  (u)  also 
bears  teeth.  The  second  or  hyoid  arch  is  modified  as  a  support 
for  the  gill-covers.  Arches  three  to  seven  support  the  gills  and 
are  known  as  gill-arches.  The  first  four  of  these  bear  spine-like 
ossifications,  the  gill-rakers,  which  act  as  a  sieve  to  intercept 
solid  particles,  and  keep  them  away  from  the  gills. 

The  appendicular  skeleton  is  represented  in  the  perch  by  a  pec- 
toral girdle  only  (Fig.  372,  Sch).  This  consists  of  a  number  of 
bones  which  lie  just  behind  the  head  on  either  side  and  furnish 
a  firm  foundation  for  the  attachment  of  the  muscles  that  move 
the  pectoral  fins.  The  fin-rays  of  the  pectoral  fin  articulate 
with  the  girdle  by  means  of  four  rod-like  bones,  the  pterygia phores 
or  radials,  and  a  number  of  small  cartilages.  There  is  no  pelvic 
girdle.  The  ventral  fins  articulate  with  a  flat  bone,  the 
hasepterygium  (Fig.  372,  Be),  which  is  probably  formed  by  the 
fusion  of  interspinal  bones  (pterygiophores). 

The  Muscular  System.  —  The  principal  muscles  are  those 
used  in  locomotion,  in  respiration,  and  in  obtaining  food.  The 
movements  of  the  body  employed  in  swimming  are  produced 
by  four  longitudinal  bands  of  muscles,  one  heavy  band  on  either 
side  along  the  back  and  a  thinner  band  on  either  side  of  both 
trunk  and  tail.  These  are  arranged  in  zigzag  myotomes. 
Weaker  muscles  move  the  gill-arches,  operculum,  hyoid,  and 
jaws. 

The  Digestive  System.  —  The  aquatic  insects,  mollusks,  and 
small  fishes  that  constitute  a  large  part  of  the  food  of  the  perch 
are  captured  by  the  jaws  and  held  by  the  many  conical  teeth. 
Teeth  are  borne  on  the  mandibles  and  premaxillae,  and  on  the 
roof  of  the  mouth.  They  are  not  used  to  masticate  the  food. 
A  rudimentary  tongue  projects  from  the  floor  of  the  mouth 


438  COLLEGE  ZOOLOGY 

cavity;  it  is  not  capable  of  independent  movement,  but  func- 
tions as  a  tactile  organ.  The  mouth  cavity  is  followed  by  the 
pharynx^  on  either  side  of  which  are  four  gill-slits.  Food  passes 
directly  to  the  stomach  through  a  short  xsophagus. 

Digestion  is  begun  in  the  stomach  by  the  fluids  secreted  by 
its  walls.  The  partially  digested  food  then  passes  through  the 
pyloric  valve  into  the  intestine.  Three  short  tubes,  called  pyloric 
cceca,  open  into  the  intestine  and  increase  its  secreting  surface. 
The  liver  lies  in  the  anterior  part  of  the  body-cavity;  its  secretion, 
the  bile,  is  stored  in  the  gall-bladder  and  then  passed  into  the 
intestine  through  the  bile-duct.  About  the  intestine,  which 
curves  slightly  in  the  body-cavity,  is  a  mass  of  fat.  Undigested 
substances  pass  out  through  the  anus.  A  large  red  gland,  the 
spleen,  is  situated  near  the  anterior  end  of  the  intestine;  it  has  no 
duct. 

The  Circulatory  System.  —  The  hlood  of  the  perch  contains 
oval  nucleated  red  corpuscles  and  ameboid  white  corpuscles.  The 
heart  lies  in  a  portion  of  the  ccelom,  the  pericardium,  beneath  the 
pharynx.  Circulation  in  the  perch  is  similar  to  that  in  the  dog- 
fish shark  (Fig.  361).  Blood  is  carried  into  the  thin- walled 
auricle  (au)  from  the  veins  through  the  sinus  venosus  (s.v). 
It  passes  into  the  muscular  ventricle  (v)  and  is  forced  by  rhyth- 
mical contractions  into  the  ventral  aorta  (v.ao)  and  thence  by 
aferent  branchial  arteries  (a.br.a)  into  the  gills.  The  aerated 
blood  is  collected  by  the  eferent  branchial  arteries  (e.br.a)  and 
conveyed  to  the  dorsal  aorta  (d.ao).  Various  parts  of  the  body 
are  supplied  by  branches  from  the  dorsal  aorta.  Oxygen  is  sup- 
plied to  the  tissues  by  the  arterial  capillaries,  and  waste  sub- 
stances are  taken  up  by  the  venous  capillaries  and  transported 
to  the  excretory  organs.  Veins  carry  the  blood  back  to  the 
heart.  Circulation  is  much  slower  in  fishes  than  it  is  in  the 
higher  vertebrates. 

The  Respiratory  System.  —  The  perch  breathes  with  four 
pairs  of  gills  supported  by  the  first  four  gill-arches.  Each  gill 
bears  a  double  row  of  branchial  filaments  (Fig.  373)  which  are 


CLASS  PISCES 


439 


abundantly  supplied  with  capillaries.  The  afferent  branchial 
artery  (Fig.  373,  K\  Fig.  361,  a.br.a)  brings  the  blood  from 
the  heart  to  the  gill- filaments;  here  an  exchange  of  gases  takes 
place.  The  carbonic  acid  gas  with  which  the  blood  is  loaded 
passes  out  of  the  gill,  and  a  supply  of  oxygen  is  taken  in  from 
the  continuous  stream  of  water  w^ich  enters  the  pharynx  through 
the  mouth  and  bathes  the  gills  on  its  way 
out  through  the  gill-slits. 

The  oxygenated  blood  is  collected  into 
the  efferent  branchial  artery  (Fig.  373,  j; 
Fig.  361,  e.br.a)  and  carried  about  the  body. 
The  gills  are  protected  from  external  injury  by 
the  gill  covering  or  operculum  (Fig.  372,  Kd) 
and  from  solid  particles  which  enter  the 
mouth  by  the  gill-rakers  (p.  437).  Because 
oxygen  is  taken  up  by  the  capillaries  of  the 
gill- filaments,  a  constant  supply  of  fresh 
water  is  necessary  for  the  life  of  the  fish. 
If  deprived  of  water  entirely,  respiration  is 
prevented,  and  the  fish  dies  of  suffocation. 

The  air-bladder  is  a  comparatively  large, 
thin-walled  sac  lying  in  the  dorsal  part  of  the 
body-cavity.  It  is  filled  with  gas  and  is  a 
hydrostatic  organ  or  "  float  " ;  in  certain 
fishes  it  may  also  aid  in  respiration.  The 
gas  contained  in  it  is  a  mixture  of  oxygen 
and  nitrogen,  and  is  derived  from  the  blood-vessels  in  its  walls. 
The  air-bladder  decreases  the  specific  gravity,  making  the  body 
of  the  fish  equal  in  weight  to  the  amount  of  water  it  displaces. 
The  fish,  therefore,  is  able  to  maintain  a  stationary  position 
without  muscular  effort.  The  amount  of  gas  within  the  air- 
bladder  depends  upon  the  pressure  of  the  surrounding  water, 
and  in  some  way  is  regulated  by  the  fish  according  to  the  depth. 
If  a  fish  is  brought  to  the  surface  from  a  great  depth,  the  air- 
bladder,  which  was  under  considerable  pressure,  is  suddenly 


Fig.  373. — Trans- 
verse section  through 
a  branchial  arch  {B), 
with  two  gill  fila- 
ments. /,  afferent 
branchial  vessel; 
2,  efferent  bran- 
chial vessel.  (From 
Schmeil.) 


440  COLLEGE  ZOOLOGY 

relieved,  and  therefore  expands,  often  forcing  the  gullet  out  of 
the  mouth. 

The  Excretory  System.  —  The  kidneys  lie  just  beneath  the 
backbone  in  the  abdominal  cavity.  They  extract  urea  and 
other  waste  products  from  the  blood.  Two  thin  tubes,  the  ure- 
ters, carry  the  excretory  matter  into  a  urinary  bladder,  where  it 
is  stored  for  a  time  and  then  expelled  through  the  urinogenital 
opening  just  posterior  to  the  anus. 

The  Nervous  System.  —  The  brain  of  the  perch  is  more  highly 
developed  than  that  of  Petromyzon  or  Squalus.  The  four  chief 
divisions  are  well  marked,  —  the  cerebrum,  optic  lobes,  cere- 
bellum, and  medulla  oblongata.  The  brain  gives  off  cranial 
nerves  to  the  sense-organs  and  other  parts  of  the  anterior  portion 
of  the  body.  The  spinal  cord  lies  above  the  centra  of  the  verte- 
bral column  and  passes  through  the  neural  arches  of  the  vertebrae. 
Spinal  nerves  arise  from  the  sides  of  the  spinal  cord. 

Sense-organs.  —  The  principal  organs  of  sense  are  the  eyes, 
ears,  and  olfactory  sacs.  The  mucous  membrane  of  the  mouth 
is  the  seat  of  the  sense  of  taste,  but  this  sense  is  not  well  developed. 
The  integument,  especially  that  of  the  lips,  serves  as  an  organ 
of  touch.  Lateral  line  organs  are  also  present,  but  their  function 
is  not  certain. 

The  two  olfactory  sacs  lie  in  the  anterior  part  of  the  skull  and 
open  by  a  pair  of  apertures  in  front  of  each  eye.  They  are  not 
connected  with  the  mouth  cavity,  and  take  no  part  in  respiration. 
The  inner  surface  is  thrown  up  into  folds  which  are  covered  with 
sense-cells.  Water  flows  in  and  out  through  the  external  open- 
ings. 

The  ear  consists  of  the  membranous  labyrinth  only.  As  in 
Petromyzon  and  Squalus,  the  sound  waves  are  transmitted  by  the 
bones  of  the  skull  to  the  fluid  within  the  labyrinth.  Three  semi- 
circular canals  (Fig.  350,  ca,  ce,  cp)  are  present,  and  the  sac- 
culus  {s)  contains  concretions  of  carbonate  of  lime,  called  ear- 
stones  or  statoliths.  The  ear  is  both  an  organ  of  hearing  and  an 
organ  of  equilibrium. 


CLASS  PISCES  441 

The  eye  of  the  perch  differs  in  several  respects  from  that  of 
terrestrial  vertebrates.  The  eyelids  are  usually  absent  in  fishes, 
since  the  water  keeps  the  eyeball  moist  and  free  from  foreign 
objects.  The  cornea  is  flattened  and  of  about  the  same 
refractive  power  as  the  water.  The  lens  is  almost  spherical. 
The  pupil  is  usually  larger  than  ^hat  of  other  vertebrates  and 
allows  the  entrance  of  more  light  rays ;  this  is  necessary, 
since  semi-darkness  prevails  at  moderate  depths.  When 
at  rest  the  eye  focuses  at  about  fifteen  inches.  To  focus 
on  distant  objects  the  lens  is  moved  back.  Fishes  cannot  see 
in  air. 

The  Reproductive  System.  —  The  sexes  are  separate.  The 
ovaries  or  testes  lie  in  the  body-cavity.  The  germ-cells  pass 
through  the  reproductive  ducts  and  out  of  the  urinogenital 
opening.  Perch  migrate  in  the  spring  from  the  deep'  waters 
of  lakes  and  ponds,  where  they  spend  the  winter,  to  the 
shallow  waters  near  shore.  The  female  lays  about  a  hundred 
thousand  eggs  in  a  long  ribbon-like  mass.  The  male  fertilizes 
the  eggs  by  depositing  spermatozoa  (milt)  over  them.  Very 
few  of  the  eggs  develop  because  of  the  numerous  animals, 
such  as  other  fishes  and  aquatic  birds,  which  feed  upon 
them. 

Development.  —  The  young  perch  hatches  from  the  egg  in 
from  two  to  four  weeks,  depending  upon  the  temperature  of  the 
water.  The  egg  passes  through  stages  similar  to  those  shown 
in  Figure  374.  A  large  part  of  the  ^^^  consists  of  yolk.  A  pro- 
toplasmic accumulation  which  forms  a  slight  projection  at  one 
end  is  called  the  germinal  disc.  The  fusion  nucleus,  resulting 
from  the  union  of  the  egg  nucleus  and  the  nucleus  brought  into 
the  egg  by  the  spermatozoon,  soon  divides,  and  two*  cells  are 
formed.  Cleavage  of  the  germinal  disc  continues  (Fig.  374, 
A ,  B)  and  the  blastoderm  (bl)  produced  gradually  grows  around 
the  yolk  (C-G).  The  embryo  (E,  emb)  appears  as  a  thickening 
of  the  edge  of  the  blastoderm.  This  grows  in  size  {F,  emb,  G) 
at  the  expense  of  the  yolk.     After  a  time  the  head  and  tail  be- 


442 


COLLEGE  ZOOLOGY 


come  free  from  the  yolk,  and  the  young  fish  breaks  out  of  the 
egg  membranes  (7) .     The  young  fish  lives  at  first  upon  the  yolk 

in  the  yolk-sac  (7,  y.s), 
but  is  soon  able  to 
obtain  food  from  the 
water.  This  consists 
of  small  crustaceans; 
insects  are  added  after 
a  time,  and  still  later 
larger  crustaceans, 
mollusks,  and  small 
fishes. 

Economic  Impor- 
tance. —  The  perch  is 
perhaps  the  best  pan- 
fish  among  American 
fresh-water  fishes.  In 
many  localities  it  is 
taken  largely  for  mar- 
ket. It  is  not  a  good 
game-fish,  but  has  one 
advantage  —  it  is  easy 
to  catch.  The  perch 
has  been  introduced 
successfully  into  sev- 
eral small  lakes  in 
Washington,  Oregon, 
and  California.    It  can 

Fig.  374.  —  Nine  stages  in  the  development    be     artificially    propa- 

t  :^:X't:/'tt.^f-  r  blas'dS;    gated,  but  other  fishes, 

emb,  embryo;    r,  thickened  edge  of  blastoderm;     sUch  aS  whitefish,  lake 
:y..     yolk-sac^       (From    Parker    and    Haswell ;  ^    pike-pCrch 

A-G,  after  Henneguy.)  '  .       . 

are  of  commercial  im- 
portance and  are,  therefore,  preferred  for  propagative  purposes 
to  the  yellow  perch. 


CLASS  PISCES  443 

2.  An  Abridged  Classification  of  Living  Fishes 

The  classification  of  fishes  is  attended  with  many  difficulties, 
since  it  is  as  yet  impossible  to  determine  the  relationships  of 
many  of  the  groups.  That  adopted  in  this  book  is  a  simplified 
arrangement  of  the  classification^  used  in  some  of  the  recent 
publications.  Synonyms  are  placed  in  parentheses  after  some 
of  the  names.  There  are  about  twelve  thousand  species  of 
fishes  known  from  the  entire  world.  Of  these  Jordan  and 
Evermann  in  their  large  four-volume  work  on  the  Fishes  of 
North  and  Middle  America  have  described  one  hundred 
and  ninety-eight  families  and  thirty-three  hundred  species 
from  the  waters  of  North  America  north  of  the  Isthmus  of 
Panama. 

Besides  the  living  fishes  there  are  a  great  many  species  known 
only  as  fossils ;  in  fact,  a  number  of  orders,  suborders,  and  fam- 
ilies contain  nothing  but  fossil  forms.  These  will  be  considered 
later  (p.  474). 

Subclass  I.    Teleostomi.    The  True  Fishes. 
Order  i.     Crossopterygii.     The  Polypteridae. 
Order  2.     Chondrostei.     The  Paddle-fishes  and  Sturgeons. 
Family  Polyodontid.e.     The  Paddle-fishes. 
Family  Acipenserid^.     The  Sturgeons. 
Order  3.     Holostei.     The  Garpikes  and  Bowfins. 
Family  Amiid^.     The  Bowfins. 
Family  Lepisosteid^.     The  Garpikes. 
Order  4.     Teleostei.     The  Bony  Fishes. 
Suborder  i.     Cypriniformes  (Ostariophysi).     The  Carp, 
Minnows,  Suckers,  and  Catfishes. 
Family  Cyprinidj^:.     The  Carp,  Minnows,  and  Suckers. 
Subfamily  Catostomin^.     The  Suckers. 
Subfamily  Cyprinin^.     The  Carp  and  Minnows. 
Family  Silurid^.     The  Catfishes. 
Suborder   2.      Clupeiformes     (Isospondyli,     Malacop- 
terygii).     The  Herrings,  Trouts,  Salmons,  etc. 


444  COLLEGE  ZOOLOGY 

Family  Elopid^.     The  Tarpons. 

Family  Clupeid^.     The  Herrings. 

Family  Salmonid^e.     The  Whitefishes,  Trouts,  and  Salm- 
ons. 
Suborder  3.     Esociformes  (Haplomi).     The  Pikes,  Cave- 
fishes,  and  Flying-fishes. 

Family  Esocid^.     The  Pikes. 

Family  Amblyopsid^.     The  Cave-fishes. 

Family  Exoccetid^.     The  Flying-fishes. 
Suborder  4.     Anguilliformes  (Apodes).    The  Eels. 

Family  Anguillid^.     The  True  Eels. 

Family  Leptocephalld^.     The  Conger  Eels. 
Suborder    5.     Symbranchiformes    (Symbranchii).     The 

SYMBRANCHiDiE  and  Amphipnoid^. 
Suborder    6.     Gasterosteiformes    (Catosteomi,    Hemi- 
BRANCHii,  Lophobranchii).    The  Sticklebacks,  Pipe- 
fishes, and  Sea-horses. 

Family  Gasterosteid^.     The  Sticklebacks. 

Family    Syngnathid.e.      The     Pipe-fishes     and     Sea- 
horses. 
Suborder    7.     Notacanthiformes    (Heteromi).     Mostly 

Deep-sea  Fishes. 
Suborder  8.     Mugiliformes  (Percesoces).    The  Silver- 
sides  and  Mullets. 
Suborder  9.     Acanthopterygii.     The  Spiny-rayed  Fishes. 

Family  Serranid^.     The  Sea-basses. 

Family  Diodontid^.     The  Porcupine  Fishes. 

Family  Percidji:.     The  Perches. 

Family  Centrarchid^.     The  Sunfishes  and  Basses. 

Family  Echeneidid^.     The  Remoras. 

Family  Lophiid^e.     The  Anglers. 

Family  Scombrid^.  .  The  Mackerels. 

Family  Xiphiid^e.     The  Swordfishes. 

Family  Pleuronectid^.     The  Flounders. 

Family  Gadid^.     The  Codfishes. 


CLASS  PISCES  445 

Subclass  II.     Dipnoi.     The  Lung-fishes. 

Family  Ceratodontid^.     The  Australian  Lung-fishes. 
Family  Lepidosirenid^e.     The     South    American     and 
African  Lung-fishes. 

3.  The  Anatomy  and  Physiology  of  Fishes  in  General 

External  Features.  —  Form  of  the  Body.  —  The  body  of 
the  majority  of  fishes  is  spindle-shaped  and  laterally  com- 
pressed, as  in  the  perch  —  a  form  that  offers  slight  resistance  to 
progress  through  the  water  (Fig.  369).  Variations  in  form  are 
correlated  with  the  habits  of  the  fish.  For  example,  the  flat- 
fishes, or  flounders,  have  thin  bodies  and  are  adapted  for  hfe  on 
the  sea  bottom;  they  are  laterally  compressed  and  swim  on  one 
side  or  the  other;  the  eels  have  a  long  cylindrical  body  which 
enables  them  to  enter  holes  and  crevices;  and  the  globe- fishes 
when  disturbed  inflate  themselves  with  air,  becoming  almost 
spherical,  in  which  condition  they  float  in  the  water.  The  shape 
of  the  head  differs  considerably  among  the  fishes;  in  the  angler- 
fish  it  is  enormous  ;  in  the  garpike  it  is  long  and  pointed;  and 
that  of  the  paddle-fish  extends  forwards  as  a  thin  paddle-like 
structure.  Many  fishes,  like  the  sea-horse  (Fig.  398)  and  some 
deep-sea  species,  are  so  curiously  shaped  as  to  show  httle  resem- 
blance to  our  common  fishes. 

Fins  and  Tail.  —  Fins  arise  in  the  embryo  as  median  and 
lateral  folds  of  the  integument  (Fig.  375,  A)  which  are  at  first 
continuous.  Later,  parts  of  the  folds  disappear  and  the  isolated 
dorsal,  caudal,  anal,  ventral,  and  pectoral  fins  persist  (Fig.  375, 
B).  There  is  a  theory  that  the  paired  fins  arise  from  gill-arches, 
but  this  method  of  origin  seems  less  probable  than  that  just 
described. 

The  ventral  fins  of  fishes  vary  considerably  in  position,  prob- 
ably because  their  skeletal  parts  are  held  only  by  muscles.  In 
the  perch  (Fig.  368)  they  are  situated  beneath  the  pectoral  fins 
and  are  said  to  be  ventral;  in  the  fresh- water  dogfish  (Fig.  384) 
they  are  just  in  front  of  the  anus  and  are  called  abdominal;  and 


446 


COLLEGE  ZOOLOGY 


in  certain  other  species  they  are  in  the  throat  region  and  are 
said  to  be  jugular  in  position.     In  most  fishes  the  fins  are  sup- 


BF  U 


Fig.  375.  —  Diagram  showing  A,  the  undifferentiated  condition  of  the  paired 
and  unpaired  fins  in  the  embryo,  and  B,  the  manner  in  which  the  permanent 
fins  are  formed  from  the  continuous  folds.  AF,  anal  fin;  An,  anus;  BF,  pelvic 
fin;  BrF,  pectoral  fin;  D,  dorsal  fin-fold;  FF,  dorsal  fin;  RF,  dorsal  fin; 
SF,  tail-fin;  S,  S,  lateral  folds  which  unite  at  S'  to  form  ventral  fold.  (From 
Wiedersheim.) 


ported,  as  in  the  perch,  by  cartilaginous  rods  and  bony  spines; 
this  type  of  appendage  is  called  an  ichthyopterygium.  In  a  few 
fishes  {e.g.  Polypterus,  Fig.  380)  the  pectoral  fins  have  a  median 

axis,  which  may  be  jointed, 

and  bears  rays  about  the 

edge ;    this   is   termed   an 

archipterygium    (Fig.  376). 

Vrhe     fingered    appendage 

/  (cheiropterygium)  of  higher 

I  vertebrates  may  have  arisen 

from  the  latter  type. 

The  shape  of  the  caudal 
fin  and  the  terminal  por- 

FiG.  376.  —  Archipterygial  pectoral    fin     tion    of    the    tail    differs   in 

of    a    lung-fish,    Neoceratodus.      B,    basal;     .i  ^  ,^„:^ ^,, ^f    ^^i,^^ 

D,  dermal;    i?,  radial.     (From  Dein,  afte;     ^he  mam  groUpS  of    fisheS, 

Howes.)  and    is    therefore    of    im- 


CLASS  PISCES  447 

portance  in  classification.  The  most  primitive  condition  is 
exhibited  by  very  few  if  any  living  fishes,  except  in  the  embryo 
or  early  larval  stages.  It  is  termed  protocercal  or  dii?hvcercal. 
and  is  symmetrical  both  externally  and  in  internal  structure 
(Fig.  377,  A).  The  second  type,  or  ^fiemcercal  tail,  is  not 
symmetrical,  and  the  vertebral  column  extends  into  the  dorsal 
lobe;  this  condition  exists  in  the  sturgeons  (Fig.  382)  and  many 
others.  The  stroke  of  the  asymmetrical  heterocercal  tail  forces 
the  anterior  part  of  the  body  downward.  This  type  is  therefore 
of  advantage  to  and  characteristic  of  those  fishes  that  have  a 


Fig.  377.  —  Two  types  of  caudal  fins.  A,  diphycercal  {Polypterus). 
B,  homocercal.  D,  dermal  fin  supports ;  N,  notochord ;  R,  radials ; 
R-\-N,  neural  spines.     (From  Dean;    A,  after  Agassiz;    B,   after  Ryder.) 

ventrally  situated  mouth  and  feed  on  the  bottom.  The  third 
type,  or  homocercal  tail,  is  externally  symmetrical  but  internally 
unsymmetrical  (Fig.  377,  B).  The  stroke  of  the  homocercal  tail 
forces  the  fish  straight  forward.  It  is  characteristic  of  fishes 
with  a  terminal  mouth  and  is  the  type  possessed  by  most  bony 
fishes. 

Fins  are  normally  used  in  locomotion  through  the  water,  but 
may  be  modified  for  other  purposes.  For  example,  the  pectoral 
fins  of  the  flying  fishes  (Fig.  394)  are  used  somewhat  like  the 
wings  of  an  aeroplane  to  sustain  the  fish  in  the  air  during  its 
leap  from  the  water;  the  pectoral  fins  of  the  African  goby  serve 
the  purpose  of  feet,  enabling  the  fish  to  move  about  on  the  ground 


448 


COLLEGE  ZOOLOGY 


in  search  of  food;  and  the  first  dorsal  fin  of  the  sucker-fish, 
Remora  (Fig.  400),  forms  a  sucker  for  the  attachment  of  its 
possessor  to  a  shark  or  turtle. 

Scales.  —  The  scales  of  fishes  form  a  protecting  exoskeleton. 
They  are  of  three  principal  types:  (i)  ganoid,  (2)  cycloid,  and 
(3)  ctenoid.  Ganoid  scales  are -usually  rhombic  in  shape  (Fig. 
371,  B).  They  have  a  superficial  covering  of  dentine  called 
ganoin.  Ganoid  scales  occur  in  most  of  the  Chondrostei  and 
HoLOSTEi,  and  these  are  often  called  ganoid  fishes.  Cycloid 
and  ctenoid  scales  are  arranged  in  overlapping  rows  as  described 
for  the  perch  (p.  434).  J^vdnid  scales  (Fig.  371,  C)  are  nearly 
circular  with  concentric  rings  about  a  central  point.  Ctenoid 
scales  (Fig.  371,  A)  are  similar  to  cycloid  scales,  but  the  part 
which  extends  out  from  under  the  neighboring  scales  bears  small 

spines.     In  many  fishes 
^t>^^^JI^i>^^  the  scales  develop   into 

^    ^  (^f^Sp  large    protective   spines, 

m  r^    -*1^^3r(^  or    may    fuse    to    form 

m^^^«§m.        bony  plates. 

Color.  —  The  general 
impression  is  that  fishes 
are  not  brightly  colored, 
but  many  of  them,  espe- 
cially in  tropical  waters, 
are  exceedingly  brilliant. 
The  colors  are  due  to 
pigments  within  special 
dermal  cells,  called  chro- 
matophores,  or  to  reflec- 
tion and  iridescence  re- 
sulting from  the  physical 
structure  of  the  scales  which  contain  crystals  of  guanin  (irido- 
cytes,'Fig.  378).  The  pigments  are  red,  orange,  yellow,  or 
black,  but  other  colors  may  be  produced  by  a  combination  of 
chromatophores;  for  example,  yellow  and  black  when  blended 


Fig.  378.  —  Chromatophores  in  skin  of 
upper  side  of  a  freshly  killed  flounder,  Pleuro- 
nectes  ftesus.  Black  bodies  represent  black 
chromatophores;  gray  bodies,  yellow;  small 
gray  plates,  iridocytes.  (From  the  Cambridge 
Natural  History,  after  Cunningham  and  Mac- 
Munn.) 


CLASS  PISCES  '  449 

give  brown.  Usually  the  colors  are  arranged  in  a  definite 
pattern  consisting  of  transverse  or  longitudinal  stripes,  and 
spots  of  various  sizes.  Coral-reef  fishes  have  long  been  famous 
for  their  brilliant  colors,  and  many  fresh-water  fishes  of  the 
temperate  zone  exhibit  bright  hues  distributed  so  as  to  form 
striking  and  intricate  patterns  (e.g.  the  rainbow  darter). 

The  contraction  and  expansion  of  the  chromatophores  of 
certain  fishes  result  in  changes  in  coloration.  These  changes 
"  are  due  to  incident  light  reflected  from  surrounding  surfaces, 
acting  through  the  visual  organs  and  the  nervous  system  on  the 
difi"erently  colored  chromatophores."  (Bridge.)  The  changes 
are  therefore  dependent  upon  the  color  of  the  fish's  environment, 
and  are  often  such  as  to  conceal  the  animal,  being  consequently 
protective.  The  change  is  slow  in  many  fishes,  but  may  be 
quite  rapid,  as  in  the  flounder.  Male  fishes  are  often  more 
brightly  colored  than  the  females,  especially  during  spawning 
activities. 

The  Skeleton.  —  The  skeleton  differs  among  the  fishes  chiefly 
in  tfie  relative  amount  of  bone  a.n<j{  cartilage.  Both  the  Teleo- 
STOMi  and  Dipnoi  possess  skeletons  which  consist  to  a  greater 
or  less  extent  of  bones  preformed  in  cartilage,  and  membrane 
bones  which  are  developed  as  dermal  ossifications.  The  ver- 
tebrcB  are  usually  amphicoelous,  as  in  the  perch,  and  bear  neural 
arches;  some  of  them  in  the  trunk  region  bear  ribs;  others  in 
the  tail  bear  haemal  arches.     There  is  no  sternum. 

The  cranium  is  independent  of  the  visceral  arches.  It  is 
complicated  in  the  teleosts  by  the  addition  of  numerous  mem- 
brane bones.  The  visceral  skeleton  consists  of  seven  arches;  five 
of  them  are  usually  gill-arches.  The  lower  jaw  articulates  with 
the  upper  jaw  and  not  directly  with  the  cranium.  The  bones 
contained  in  the  gill-cover  or  operculum  develop  from  the  hyoid 
arch. 

The  Digestive  System.  —  The  food  of  our  common  fishes 
consists  of  vegetation,  insect  larvae,  crustaceans,  mollusks,  and 
other  smaller  fishes.     Some  fishes  are  voraciously  carnivorous, 

2  G 


450  COLLEGE  ZOOLOGY 

and,  like  the  sharks,  attack  animals  larger  than  themselves; 
others  are  herbivorous  to  a  considerable  extent,  feeding  on 
seaweeds  and  other  vegetation ;  and  still  others  act  as  scavengers 
or  swallow  mud  from  which  both  living  and  dead  organisms  are 
obtained. 

Fishes  are  ultimately  dependent  upon  microscopic  organisms, 
as  is  illustrated  by  the  following  example  :  — 

"  On  the  morning  of  July  23  there  was  taken  a  large  specimen 
(squeteague)  whose  stomach  contained  an  adult  herring.  In 
the  stomach  of  the  herring  were  found  two  young  scup  (besides 
many  small  Crustacea),  and  in  the  stomach  of  one  of  these  scup 
were  foimd  copepods,  while  in  the  alimentary  tract  of  these  last, 
one  could  identify  one  or  two  of  the  diatoms  (unicellular  plants) 
and  an  infusorian  test  among  the  mass  of  triturated  material 
which  formed  its  food."     (Peck.) 

Most  fishes  possess  teeth  on  the  jaws,  roof  of  the  mouth,  or 
gill-arches.  These  are  used  principally  for  holding  food,  but 
in  some  cases  for  mastication.  The  most  primitive  type  of 
tooth  is  a  simple  pointed  cone.  Some  fishes  have  front  teeth 
for  capturing  prey  and  back  teeth  for  crushing;  and  in  others 
the  teeth  are  all  modified  for  crushing.  Teeth  that  are  lost  or 
worn  away  are  generally  replaced. 

The  alimentary  canal  is  usually  similar  to  that  of  the  perch. 
Gastric  glands  in  the  walls  of  the  stomach  secrete  digestive 
juices.  The  intestine  often  possesses  blind  pouches,  the  pyloric 
caeca,  which  increase  the  secretory  surface. 

The  Circulatory  System.  —  Circulation  in  fishes  is  essentially 
like  that  already  described  (Fig.  361).  Lymph  spaces  and  lymph 
capillaries  are  situated  in  various  parts  of  the  body;  they  collect 
blood  plasma  from  the  tissues  and  transport  it  to  the  veins. 

The  body  of  the  fish  contains  several  ductless  glands  which 
may  be  considered  under  the  circulatory  system.  The  functions 
of  these  glands  are  not  well  known.  The  extirpation  of  them 
results  in  serious  disturbances,  and,  in  some  cases,  death.  They 
secrete  substances  (internal  secretions)  directly  into  the  blood 


CLASS  PISCES 


451 


or  lymph.  The  thyroid  is  homologous  to  the  endostyle  of  tuni- 
cates  (p.  391)  and  Amphioxus  (p.  396).  It  lies  in  the  branchial 
region  and  is  paired.  The  thymus  is  situated  dorsally  in  the 
branchial  region.  The  sHeen  is  a  large  gland  usually  lying  near 
the:  stomach ;  colorless  blood  corpuscles  are  formed  in  it,  and  old 
red  corpuscles  are  destroyed  by^it.  The  suprarp/nal  bodies  are 
situated  close  to  the  kidneys. 

The  Respiratory  System.  —  Respiration  takes  place  in  the 
gills,  and,  in  the  Dipnoi  and  some  teleosts,  also  to  some  extent 


Fig.  379.  —  Diagram  illustrating  the  mechanism  of  respiration  in  teleosts. 
A,  phase  of  inspiration.  B,  phase  of  expiration.  (From  Wiedersheim,  after 
Dahlgren.) 


in  the  air-bladder.  During  respiration  in  teleosts  the  walls  of  the 
mouth  act  like  a  pump  (Fig.  379).  In  inspiration  (A)  the  oral 
cavity  (cav.oris)  is  enlarged  by  the  raising  of  the  opercular 
apparatus,  and  water  is  therefore  drawn  into  it  through  the 
mouth.     Folds   of   mucous   membrane    (branchiostegal   mem- 


452  COLLEGE  ZOOLOGY 

branes)  prevent  water  from  entering  through  the  opercular 
aperture.  Expiration  {B)  results  from  the  contraction  of  the 
opercular  apparatus;  the  branchiostegal  membrane  is  opened 
and  water  passes  out  through  the  gill-slits.  The  exit  of  water 
by  way  of  the  mouth  is  prevented  by  valves  of  mucous  mem- 
brane (maxillary  and  mandibular  valves). 

4.   General  Account  of   Some  of  the  Principal  Groups 

OF  Fishes 

Subclass  I.  Teleostomi.  —  To  the  Teleostomi  belong  the 
majority  of  fishes.  The  four  orders  of  living  forms  are  unequal 
in  number  of  species,  most  of  which  belong  to  the  Teleostei. 

Order  i,  Crossopterygii.  —  Most  of  the  Crossopterygii 
are  extinct,  and  the  order  contains  only  one  family  and  two 


Fig.  380.  —  Polypterus  senegalus.     (From  the  Cambridge  Natural  History.) 

genera  of  living  forms.  One  species,  Polypterus  senegalus  (Fig. 
380),  lives  in  the  Nile.  It  is  of  special  interest  to  morphologists 
because  it  presents  many  structural  features  characteristic  of 
ancient  crossopterygians. 

Order  2.  Chondrostei.  —  This  order  contains  the  sturgeons 
and  paddle- fishes.  These  have  a  skeleton  largely  of  cartilage, 
a  heterocercal  tail,  ganoid  scales  (Fig.  371,  B),  and  abdominal 
pelvic  fins. 

The  family  Polyodontid^  contains  two  species  of  paddle- 
fishes,  Polyodon  spathula  (Fig.  381)  of  the  Mississippi  Valley, 
and  Psephurus  gladius  of  the  Yang-tse-Kiang  in  China.  Poly- 
odon reaches  a  length  of  six  feet  and  a  weight  of  one  hundred 
and  sixty  pounds,  but  the  specimens  usually  taken  weigh  no 
more  than  fifty  pounds.  Its  large,  paddle-shaped  snout  is  re- 
garded as  a  sense-organ,  and  its  use  is  still  unknown.     The 


CLASS   PISCES 


453 


food  of  Polyodon  consists  largely  of  minute  plants  and  ani- 
mals, of  which  enormous  numbers  are  devoured.     The  paddle- 


FlG. 


381.  —  The  spoonbill  sturgeon  or  paddle- fish,  Polyodon  spathula, 
ventral  and  side  view.     (From  Dean,  after  Goode.) 


fish  is  good  to  eat,  but  its  roe,  from  which  caviar  is  made,  is  more 
valuable  than  its  flesh. 

The  family  AciPENSERiDiE  contains  two  genera  of  sturgeons, 
Acipenser  and  Scaphirhynchus.  They  inhabit  the  seas,  lakes, 
and  rivers  of  Europe,  Asia,  and  America.  Sturgeons  possess  a 
cephalic  prolongation  or  rostrum  which  bears  on  its  ventral 
surface  a  number  of  tactile  filaments  called  barbels.  The 
scales  form  five  longitudinal  rows  of  bony  scutes  between  which 
are  smaller  ossifications.     The  mouth  lacks  teeth.     The  common 


Fig.  382. 


The  common  sturgeon,  Acipenser  sturio. 
after  Goode.) 


(From  Dean, 


sturgeon,  Acipenser  sturio  (Fig.  382),  lives  along  the  Atlantic 
coast  arid  ascends  the  rivers  of  northern  Europe  and  the  United 
States.  Acipenser  rubicundus  is  the  sturgeon  of  the  rivers  and 
lakes  of  the  middle  west.     It  feeds  on  the  bottom,  using  its  snout 


454  COLLEGE  ZOOLOGY 

for  stirring  up  the  mud  and  its  barbels  for  locating  snails,  cray- 
fishes, and  insect  larvae.  Sturgeon  flesh  is  a  valued  article  of 
food,  the  eggs  are  made  into  caviar,  and  the  air-bladders  furnish 
isinglass. 

Order  3.  Holostei.  —  Most  of  the  Holostei  are  extinct; 
only  two  of  the  eight  families  have  living  representatives, 
namely  the  LEPisosxEiDiE  or  garpikes,  and  the  Amiid^  or  bow- 
fins.  These  fishes  are  called  bony  ganoids,  since  the  skeleton 
is  bony  and  the  scales  are  often  ganoid.  In  some  the  scales  are 
cycloid  (Fig.  371).  The  tail  is  diphy cereal  or  homocercal,  with 
a  tendency  toward  the  heterocercal  type,  and  the  ventral  fins 


Fig.  383.  —  The  alligator-gar,  Lepisosteus  tristcechus.     (From  Jordan 
and  Evermann.) 

are  abdominal.  The  living  species  of  garpikes  and  bowfins  are 
known  only  from  America. 

The  garpikes  belong  to  the  genus  Lepisosteus.  There  are 
three  common  species,  the  long-nosed  garpike,  the  short-nosed 
gar,  and  the  alligator  gar  (Fig.  383).  The  long-nosed  gar,  Lepi- 
sosteus osseus,  is  common  in  the  lakes  and  rivers  of  the  United 
States.  It  is  about  four  feet  long.  The  body  is  slender  with  an 
extended  beak,  at  the  end  of  which  are  the  nostrils.  Its  heavy 
ganoid  scales  effectively  protect  it  from  every  other  living  crea- 
ture in  the  water.  Garpikes  are  voracious,  devouring  minnows, 
young  fish,  and  other  aquatic  animals,  and  where  they  occur  in 
large  numbers  are  very  harmful  to  the  fishing  industry. 

Amia  (Amiatus)  calva,  the  mudfish,  fresh- water  dogfish,  or 
bowfin  (Fig.  384),  is  the  only  existing  representative  of  the  family 
AMiiDiE.    It  inhabits  the  sluggish  waters  of  the  Great  Lakes  region 


^ 


CLASS   PISCES 


455 


and  the  Mississippi  Valley.  The  body  is  about  a  foot  and  one 
half  long,  is  dark  olive  in  color,  and  bears,  in  the  male,  a  black  spot 
at  the  base  of  the  caudal  fin.  It  is  very  voracious,  feeding  on  fish, 
crayfishes,  mollusks,  and  other  aquatic  animals.  The  breeding 
season  is  in  April,  May,  or  June,  according  to  the  latitude.  The 
male  clears  a  space  in  the  vegetcttion  of  a  quiet  inlet  in  which 
the  eggs  are  laid,  and  then  guards  the  nest  (Fig.  384)  during 


Fig.  384.  — The  fresh-water  dogfish  or  bowfin,  Amia  {Amiatus)  calva,  and 
its  nest.     (From  the  Cambridge  Natural  History,  after  Dean.) 


the  hatching  period  of  from  eight  to  ten  days,  and  while  the 
young  remain  in  the  nest  —  about  nine  days  more.  The  male 
accompanies  the  young  when  they  leave  the  nest,  and  con- 
tinues to  guard  them  until  they  reach  a  length  of  about  four 
inches. 

Order  4.  Teleostei.  —  This  order  contains  the  majority  of 
living  species,  the  bony  fishes.  The  skeleton  is  extensively 
ossified;  the  tail  is  usually  homocercal  (Fig.  377,  B)\  and  the 
scales  are  cycloid  or  ctenoid  (Fig.  371).  Space  will  allow  a 
few  notes  on  only  about  one  eighth  of  the  families  of  fishes 
included  in  the  order. 


456 


COLLEGE  ZOOLOGY 


Family  i.   Cyprinid^e. — The  Carp,  Minnows,  and  Suckers. 

Subfamily  Catostomin^e." — The  Suckers.  Most  of  the 
suckers  are  inhabitants  of  the  fresh  waters  of  North  America; 
two  of  the  seventy  or  more  species  occur  in  Asia.  Their  mouths 
are  usually  very  protractile  and  possess  fleshy  lips.  They  feed 
on  the  bottom,  eating  vegetation,  worms,  insect  larvae,  and  other 
soft-bodied  animals.  In  the  spring  suckers  swim  upstream 
to  spawn.  The  sucker  is  barely  edible,  but  is  nevertheless  an 
important  commercial   fish.-    The   common   or  white   sucker, 


Fig.  385.  —  The  common  sucker,  Catostomus  commersoni.     (From  Jordan 
and  Evermann.) 


Catostomus  commersoni  (Fig.  385),  is  very  widely  distributed. 
This  subfamily  includes,  besides  the  suckers,  the  red-horses, 
buffaloes,  quillbacks,  and  fresh-water  mullets. 

Subfamily  Cyprinin^.  —  There  are  about  two  hundred 
genera  and  a  thousand  species  of  fishes  belonging  to  this  sub- 
family. About  two  hundred  and  twenty- five  species  occur  in  the 
United  States.  They  are  mostly  small,  but  should  not  be  mis- 
taken for  young  fish  on  that  account.  The  chubs,  hornyheads, 
fall- fish,  and  squaw  fish  are  common  in  various  parts  of  the 
country.  The  German  carp  (Fig.  386)  was  introduced  into 
North  America  in  1872,  and  is  now  firmly  established  in  our 
waters.  It  will  live  in  muddy  ponds  and  streams,  is  prolific, 
grows  rapidly,  and  is  edible,  although  not  very  good.  Since  its 
introduction  it  has  been  accused  of  driving  away  other  fishes,  of 


CLASS   PISCES 


457 


making  clear  lakes  muddy,  of  eating  wild  celery  and  grasses  on 
which  ducks  feed,  and  of  devouring  the  eggs  of  other  fishes. 


Fig.  386.  —  The  carp,  Cyprinus  carpio.     (From  Lankester's  Treatise, 
after  Seeley.) 

Family  2.  Silurid^e.  —  The  Catfishes.  These  are  mostly 
fresh-water  fish,  about  thirty  species  of  which  are  known  from  the 
United  States.  The  body  of  the  catfish  is  naked;  the  head  bears 
eight  barbels;  and  there  is  a  short,  fatty,  adipose  fin  back  of  the 


Fig.  387.  —  The  bullhead  or  catfish,  Ameiurus  melas.     (From  Dean, 
after  Goode.) 

dorsal  fin.  The  bullhead  or  horned  pout,  Ameiurus  nebulosus, 
is  a  common  fish  in  the  ponds  and  streams  of  the  North  and 
East.     The  black  bullhead,  Ameiurus  melas  (Fig.  387),  is  found 


458 


COLLEGE  ZOOLOGY 


chiefly  west  of  the  Mississippi  River.  The  bullhead  is  tenacious 
of  life  and  can  live  out  of  water  for  some  time.  The  blue  or 
Mississippi  catfish,  Ictalurus  furcatus,  is  a  valuable  food-fish. 
It  inhabits  the  sluggish  waters  of  the  streams  of  the  Mississippi 
Valley  and  Gulf  States,  and  is  the  largest  member  of  the  family, 
sometimes  reaching  a  length  of  five  feet  and  attaining  a  weight 
of  over  one  hundred  pounds.  Another  large  species  is  the  chan- 
nel or  spotted  catfish,  Ictalurus  punctatus.  It  occurs  in  the 
Great  Lakes  region  and  Mississippi  Valley,  and  prefers  clear, 
flowing  water. 

Family  Elopid^e.  —  The  Tarpons.     There  are  four  or  five 
species  of  tarpons  inhabiting  the  tropical  seas.     The  common 


Fig.  388. 


The  tarpon,   Tarpon  atlanticus.     (From  the  Cambridge  Natural 
History,  after  Goode.) 


tarpon.  Tarpon  atlanticus  (Fig.  388),  is  a  famous  game-fish  on 
the  coast  of  Florida,  and  is  called  the  "  silver  king." 

Family  Clupeid^.  —  The  Herrings.     The  members  of  this 
family  are  mostly  salt-water  forms.     They  are  not  game-fishes, 


,.^iSS^0 


Fig.  389.  —  The  herring,   Clupea  harengus.      (From  Jordan  and  Evermann.) 


CLASS  PISCES  459 

but  about  ten  species  are  of  commercial  value.  The  common 
herring,  Clupea  karengus  {Fig.  389),  is  "  the  most  important  of 
the  food-fishes  in  the  Atlantic."  (Jordan  and  Evermann.) 
Herring  swim  about  the  North  Atlantic  in  immense  shoals,  often 
covering  half  a  dozen  square  miles  and  containing  as  many  as 
three  billion  individuals.  On  tlte  New  England  coast  herring 
are  smoked,  salted,  pickled,  packed  as  sardines,  or  serve  as  bait 
for  cod- fishing. 

Family  Salmonid^.  —  The  Whitefishes,  Salmons,  and  Trouts. 
Many  of  our  most  important  food  and  game  fishes  belong  to  this 


Fig.  390.  —  The  whitefish,  Coregonus  clupeiformis.     (From  Jordan 
and  Evermann.) 

family,  such  as  the  mountain  trout,  rainbow-trout,  and  steel- 
head  trout  of  the  West,  the  lake-trout  and  common  whitefish  of 
the  Great  Lakes,  the  brook  trout  of  the  East,  the  Atlantic  salmon 
of  Europe  and  North  America,  and  the  quinnat  or  chinook 
salmon,  the  blueback  or  sockeye  salmon,  and  the  silver  or  coho 
salmon  of  the  Pacific.  These  fishes  are  easily  reared,  and 
millions  of  their  eggs  or  young  are  distributed  each  year  by  the 
United  States  Bureau  of  Fisheries  (see  Table  XV). 

The  common  whitefish,  Coregonus  clupeiformis  (Fig.  390), 
occurs  throughout  the  Great  Lakes  region.  During  the  winter 
it  prefers  deep  water,  but  in  the  spring  it  migrates  to  the  shallow 
w^ater  to  secure  insect  larvae  which  become  abundant  at  that 


460  COLLEGE  ZOOLOGY 

time.  It  migrates  to  shallow  water  again  in  the  autumn  to 
spawn.  The  mouth  is  on  the  under  side,  and  the  crustaceans, 
mollusks,  and  other  animals  used  as  food  are  picked  up  from  the 
bottom.  The  eggs  are  laid  over  honeycomb  rock,  and,  since 
many  of  them  are  covered  by  sediment  or  fall  prey  to  mud- 
puppies,  yellow  perch,  crayfishes,  and  other  enemies,  very  few 
reach  the  adult  stage.  Because  of  this  fact  the  government  each 
year  gathers,  rears,  and  distributes  millions  of  whitefish  eggs. 
White  fishes  are  captured  in  deep  water  by  means  of  gill-nets 
which  hold  the  fish  just  behind  the  gill-covers.  The  average 
weight  is  about  four  pounds,  but  they  may  become  as  heavy  as 
twenty  pounds. 

The  lake-trout,  Cristivomer  namaycush,  is  another  important 
food-fish  of  the  Great  Lakes  region.  It  is  the  largest  of  our 
trouts,  averaging  about  eighteen  pounds,  but  occasionally  attain- 
ing a  weight,  of  over  one  hundred  pounds.  Lake-trout  are  cap- 
tured usually  in  gill-nets.  They  are  omnivorous,  but  show 
special  preference  for  lake  herring.  The  spawning  season  ranges 
from  September  to  November,  according  to  the  latitude.  Mil- 
lions of  eggs  are  cared  for  and  distributed  by  the  government 
each  year. 

The  brook  or  speckled  trout,  Sahelinus  fontinalis,  is  one  of 
our  most  beautiful  and  well-known  game-fishes.  It  prefers  clear, 
cool  streams  with  a  swift  current  and  a  gravelly  bottom. 

The  mountain  or  cut- throat  trout,  Salmo  clarkii,  is  a  large 
species  inhabiting  the  streams  and  lakes  of  the  Rocky  Mountain 
region.  The  rainbow-trout,  Salmo  irideus,  is  also  a  Western 
species.  It  is  a  good  game-fish  and  takes  the  fly  readily.  In 
weight  it  averages  about  two  or  three  pounds.  The  steelhead 
or  salmon  trout,  Salmo  gairdneri,  is  found  in  the  streams  along 
the  Pacific  coast.  Like  the  salmon  it  migrates  upstream  to 
spawn.  Its  average  weight  is  about  eight  pounds.  Thousands 
of  steelhead  trout  are  taken  each  year  for  canning  purposes, 
especially  in  the  Columbia  River.  They  are  also  considered 
excellent  game-fish. 


CLASS  PISCES 


461 


The  chinook  or  quinnat  salmon,  Oncorhynchus  tschawytscha 
(Fig.  391),  is  the  most  important  commercial  fish  of  the  family. 
It  lives  in  the  sea  along  the  Pacific  coast  "  from  Monterey  Bay, 
California,  and  China,  north  to  Bering  Straits."  It  enters  the 
fresh- water  streams  to  spawi;^,  especially  the  Sacramento, 
Columbia,  and  Yukon  rivers.  The  ascent  takes  place  in  the 
spring  and  summer,  beginning  in  February  or  March  in  the 
Columbia  River.  The  salmon  do  not  feed  during  this  migra- 
tion, but  swim  at  first  slowly  and  then  more  rapidly  until  they 
reach  the  small,  clear,  mountain  streams  often  more  than  a 
thousand  miles  from   the   sea.     Spawning  occurs  from  July  to 


r 


Fig.  391. 


V' 


Quinnat  salmon  (female).     Oncorhynchus  tschawytscha. 
(From  Jordan  and  Evermann.) 


December,  according  to  the  temperature  of  the  water,  which 
apparently  must  be  below  54°  Fahr.  The  eggs  are  deposited 
upon  the  gravelly  bottoms  of  the  streams,  after  which  both 
males  and  females  die;  consequently  an  individual  spawns  only 
once  during  its  lifetime.  The  eggs  hatch  in  about  seven  weeks, 
and  the  young  remain  on  the  spawning  ground  for  six  weeks. 
They  then  float  slowly  do\ynstream  and  may  be  four  or  five 
inches  long  when  they  reach  the  sea.  The  adults  are  captured 
by  gill-nets  and  other  devices  as  they  ascend'  the  rivers,  and  are 
considered  the  most  important  of  all  commercial  fishes.  The 
government  is  artificially  propagating  the  chinook  salmon, 
otherwise  its  numbers  would  soon  be  materially  decreased. 


462 


COLLEGE  ZOOLOGY 


Family  Esocid^.  —  The    Pikes.      There  is  one  genus  with 
seven  species  of  pikes;  all  of  them  occur  in  North  America.     The 


Fig.  392.  —  The  pike,  Esox  lucius.     (From  Jordan  and  Evermann.) 

common  pike  or  pickerel,  Esox  lucius  (Fig.  392),  inhabits  "  all 
suitable  fresh  waters  of  northern  North  America,  Europe,  and 
Asia."  It  is  extremely  voracious,  feeding  on  other  fishes,  frogs, 
aquatic  birds,  and  many  other  aquatic  animals.  The  pike  is  an 
excellent  game-fish,  but  its  flesh  is  not  very  good.  The  muskal- 
lunge,  Esox  masquinongy,  resembles  the  pike  in  form  and  habits. 
It  is  found  in  the  Great  Lakes  region  and  is  a  king  among  fresh- 
water game-fishes,  reaching  a  length  of  over  seven  feet  and  a 
weight  of  almost  a  hundred  pounds. 

Family   Amblyopsid^e.  —  The    Cave-fishes.     There   are   six 
species  of  cave-fishes  known  from  the  subterranean  streams  of  the 


Fig.  393.  —  A  cave- fish,  Amblyopsis  spelceus.     (From  Lankester's  Treatise, 
after  Jordan  and  Evermann.) 


cave  region  of  Indiana,    Kentucky,    and   Missouri.     They  are 
small  fish,  but  are  of  special  interest  because  the  eyes  of  some  of 


CLASS  PISCES 


463 


them  are  rudimentary  and  covered  with  a  thick  skin.  Amhly op- 
sis  spelceus  (Fig.  393)  is  common  in  the  river  Styx  of  the  Mam- 
moth Cave. 

Family  Exoccetid^.  — The  Flying-fishes  (Fig.  394).     There 
are  about   sixty- five   species   in  this   family,  inhabiting  warm 


Fig.  394.  —  A  flying  fish,  Exocoetus  callopterus. 
after  Giinther.) 


(From  Lankester's  Treatise, 


seas.  Some  of  them  are  able  to  leave  the  water,  and,  rising  in  the 
air  a  few  feet,  "  fly  "  a  distance  of  from  a  few  rods  to  more  than 
an  eighth  of  a  mile.  It  seems  probable  that  the  pectoral  fins 
do  not  force  the  fish  forward,  but  simply  sustain  the  body  in  the 
air. 

Family  Anguillid^.  — The  Eels.     The  true  eels  should  not* 
be  confused  with  the  lamprey  eels  of  the  class  Cyclostomata 


Fig.  395.  —  The  common  eel,  Anguilla  rostrata.     (From  Jordan  and 
Evermann.) 


(p.  414).     The  single  species  of  eel,  Anguilla  rostrata  (Fig.  395), 
in  North  America  occurs  in  the  streams  of  the  Atlantic  coast. 


464 


COLLEGE  ZOOLOGY 


It  is  long  and  slender,  and  its  scales  are  inconspicuous.  The 
dorsal,  caudal,  and  anal  fins  are  continuous.  The  eels  enter  the 
sea  in  the  autumn  to  spawn,  after  which  they  die.  The  eggs  are 
deposited  on  mud-banks  usually  near  the  mouths  of  rivers.  The 
young  develop  in  the  sea  and  then  migrate  up  the  rivers.  Eels 
are  considered  by  many  a  good  article  of  food,  and  are  therefore 
of  commercial  value. 

Family    Gasterosteid^.  -^  The    Sticklebacks.     These    are 
small  fishes  famous  for  their  nest-building  habits.     The  common 


Fig..  396.  —  The  two-spined  stickleback,  Gasterosleus 
bispinosus.  Above,  nest  with  eggs,  and  male  entering. 
Below,  male  depositing  its  milt  on  the  eggs.  (From 
Davenport.) 

Eastern  stick\eba,ck,  Gasterosleus  bispinosus  (Fig.  396),  has  two 
large  spines  preceding  the  dorsal  fin.     The  nest  is  built  of  sticks 


CLASS  PISCES 


465 


fastened  together  with  threads  secreted  by  a  gland  in  the  male. 
The  female  lays  eggs  in  the  nest;  the  male  then  enters  and 
fertilizes  them,  after  which  he  guards  them  from  intruders. 


Fig.  397.  —  The  pipe-fish,  Syngnathus  acus.     (From  Lankester's  Treatise, 
after  Gunther.) 


Family  Syngnathid^.  —  The  Pipe-fishes  and  Sea-horses. 
The  pipe-fishes  (Fig.  397)  are  extremely  thin,  with  a  tubular 
snout,  abbreviated  fins,  and  a  covering  of 
bony  armor.  Their  food  is  captured  by  in- 
serting the  snout  into  the  cavities  in  sponges 
and  corals,  and  by  picking  off  minute  ani- 
mals from  the  branches  of  seaweeds.  The 
sea-horses  (Fig.  398)  are  small  species  that 
do  not  look  much  like  fish,  the  head  remind- 
ing one  of  the  head  of  a  horse.  They 
swim  by  means  of  the  dorsal  fin,  hold- 
ing themselves  in  a  vertical  position  as  in 
Figure  398.  They  cling  to  objects  with 
their  prehensile  tail.  The  eggs  are  carried 
in  a  brood  pouch  (mp)  of  the  male  until 
they  hatch. 

Family  Serranid^e.  —  The  Sea-basses. 
This  is  a  large  family  containing  over  four 
hundred  species,  mostly  marine.  The  white 
lake  bass,  Roccus  chrysops,  is  a  fresh- water 
species  of  the  Great  Lakes  region.  The 
2  H 


Fig.  398.— The  sea- 
horse, Hippocampus 
guttulatus,  male. 
a,  anus;  b.a,  branchial 
aperture;  m.p,  brood- 
pouch.  (From  the 
Cambridge  Natural 
History.) 


466 


COLLEGE  ZOOLOGY 


striped  bass,  Roccus  lineatus,  is  a  fine  game-fish  occurring  along 
the  coast  of  eastern  North  America.  It  has  also  been  success- 
fully introduced  along  the  coast  of  California.  The  jewfish  or 
black  sea-bass,  Stereolepis  gigas,  is  the  giant  game-fish  of  the 
California  coast.  It  can  be  taken  with  a  sixteen-ounce  rod, 
and  there  are  many  records  of  specimens  captured  by  this 
method  weighing  over  three  hundred  pounds. 

Family    Diodontid^e.  —  The     Porcupine-fishes.     These    in- 
habitants of  tropical  seas  are  covered  with  movable  spines, 


Fig.  399. 


The  porcupine  fish,  Diodon  maculatus.     A,  normal;  B,  inflated. 
(From  Lankester's  Treatise,  after  Giinther.) 


hence  their  name.  They  live  on  the  bottom  among  seaweeds 
and  corals,  and  when  disturbed  inflate  their  bodies  by  swallow- 
ing air  (Fig.  399).  They  then  float  belly  upward,  in  which  con- 
dition they  are  not  easily  injured  by  their  enemies. 


CLASS   PISCES  467 

Family  PERCiDiE.  —  The  Perches.  The  perch  family  contains 
a  large  number  of  small  fresh- water  fishes,  most  of  which  are  of 
little  economic  importance.  The  yellow  perch,  Perca  flavescens, 
was  chosen  as  a  type  of  the  class  (pp.  432-442).  The  wall-eyed 
pike  or  pike-perch,  Stizostedion  vitr^um,  is  another  well-known  and 
valuable  species.  It  is  common  in  the  Great  Lakes  region  and  is  ex- 
tensively propagated  by  the  Bureau  of  Fisheries  (see  Table  XV). 

Family  Centrarchid^.  —  The  Basses,  Grapples,  and  Sun- 
fishes.  These  fishes  inhabit  the  fresh  waters  of  North  America. 
There  are  about  thirty  species,  most  of  which  are  good  game- 
fishes  and  also  excellent  for  the  table.  Some  of  the  most  com- 
mon species  are  the  crappie,  Pomoxis  annularis,  the  rock-bass, 
Amhloplites  rupestris,  the  bluegill,  Lepomis  pallidus,  the  com- 
mon sunfish  or  pumpkin-seed,  Eupomotis  gibbosus,  the  small- 
mouthed  black  bass,  Micropterus  dolomieu,  and  the  large- 
mouthed  black  bass,  Micropterus  salmoides.  The  small-mouthed 
black  bass  is  considered  ''  inch  for  inch  and  pound  for  pound, 
the  gamest  fish  that  swims."  (Henshall.)  The  male  bass  in 
May  or  June  makes  a  nest  by  clearing  away  a  place  near  shore 
where  there  are  good-sized  stones.  Eggs  are  then  laid  and  fer- 
tilized, and  the  male  guards  them  during  the  hatching  period  of 
five  or  §ix  days.  The  male  continues  to  protect  the  young 
until  they  reach  a  length  of  an  inch  and  a  quarter.  Black  bass 
are  successfully  propagated  in  artificial  ponds  by  the  Bureau 
of  Fisheries  (see  Table  XV). 

Family  Echeneidid.e. — The  Remoras  (Fig.  400).  This 
family  contains  about  a  dozen  species  of  peculiar  fishes  that  live 


Fig.  400.  —  A  sucking  fish,  Remora  brachyptera.     (From  the  Cambridge 
Natural  History,  after  Goode.) 


468  COLLEGE  ZOOLOGY 

in  tropical,  warm  seas.  The  first  dorsal  fin  is  modified  to  form 
a  sucker  by  means  of  which  the  fish  attaches  itself  to  sharks, 
turtles,  whales,  other  large  aquatic  animals,  and  floating  objects 
such  as  boats.  They  are  able  to  swim,  but  prefer  to  be  carried 
about  by  other  animals.  Their  food  consists  of  other  fish  and 
probably  of  the  scraps  obtained  when  the  shark,  or  other  animal 
to  which  the  individual  is  attached,  has  a  meal. 

Family  Lophiid^.  —  The  Anglers.     Living  on   the  bottom 
of  the  Atlantic,  Indian,  and  Pacific  oceans  are  about  a  dozen 


Fig.  401.  —  The  fishing-frog  or  angler,  Lophius  piscatorius.     (From 
Sedgwick's  Zoology,  after  Cuvier.) 

species  of  extremely  large-mouthed  fishes  known  as  anglers. 
Lophius  piscatorius,  the  fishing-frog  or  goose-fish  (Fig.  401), 
occurs  on  the  coast  of  North  America.  It  is  said  to  lie  on  the 
bottom  with  its  mouth  open  and  to  use  its  long  first  dorsal  ray, 
which  is  inserted  on  the  snout,  as  a  bait  to  attract  other  fishes 
into  its  mouth  cavity.  It  reaches  a  length  of  over  three  feet  and 
has  a  mouth  more  than  a  foot  wide. 

Family  Scombrid^.  —  The  Mackerels.  There  are  about 
sixty  species  of  food- fishes  belonging  to  this  family,  fifteen  of 
which  inhabit  the  salt  waters  of  North  America.  The  common 
mackerel.  Scomber  scombrus   (Fig.  402),  occurs  in  the  North 


CLASS   PISCES  469 

Atlantic,  swimming  about  in  enormous  schools.  It  feeds  on 
small  aquatic  animals,  such  as  Crustacea,  and  furnishes  food 
for  other  fishes.  It  is  also  a  valuable  food-fish  for  man.  The 
Spanish  mackerel,  Scomheromorus  maculatus,  is  also  a  common 
food-fish  of  the  North  Atlantic.  The  tuna,  Thunnus  thynnus, 
is  called  the  tunny  or  horse-mackei^l  on  our  eastern  coast,  but 
is  the  tuna  of  California.     They  are  eagerly  sought  with  hook 


r 

Fig.  402.  —  The  mackerel,  Scomber  scombrus.     (From  Jordan  and  Evermann.) 

and  line,  and  many  have  been  landed  by  this  means  that  weighed 
over  one  hundred  pounds. 

Family  Xiphiid.^.  —  The  Swordfishes.  The  single  species, 
Xiphias  gladius,  belonging  to  this  family  is  widely  distributed 
in  salt  waters.  It  reaches  a  maximum  weight  of  about  six  hun- 
dred pounds,  and  its  prolonged  upper  jaw  makes  it  a  formidable 
foe.  Sometimes  fishing  boats  are  pierced  and  sunk  by  the 
sword  of  large  individuals.  The  food  of  the  swordfish  consists 
of  squids,  mackerel,  menhaden,  and  other  fish,  and  it  in  turn  is 
a  valuable  article  of  food  for  man. 

Family  Pleuronectid^.  —  The  Flounders.  These  are  flat- 
fishes known  as  flounders,  halibuts,  soles,  plaice,  and  turbots. 
They  are  flattened  from  side  to  side,  and  thus  adapted  for  life 
on  the  sea  bottom.  Frequently  they  are  colored  on  the  upper 
surface  so  as  to  resemble  the  sand  or  other  material  surrounding 
them.  The  young  flatfish  resembles  an  ordinary  fish  when  it 
hatches,  but  it  soon  begins  to  broaden  laterally  and  swim  on  its 
side,  while  the  eye  on  the  lower  side  moves  around  to  the  upper 


470 


COLLEGE  ZOOLOGY 


side.  The  common  halibut,  Hippoglossus  hippoglossus,  and  the 
winter  flounder,  Pseudopleuronectes  americanus  (Fig.  403),  are 
important  American  food- fishes. 


Fig.  403.  —  The  flounder,  Pseudopleuronectes  americanus.      (From  Dean, 
after  Goode.) 

Family  Gadid^e. — The  Codfishes.  Many  of  our  most  im- 
portant food-fishes,  the  pollacks,  codfishes,  haddocks,  and  hakes, 
belong  to  this  family.  The  common  codfish  is  Gadus  callarias 
(Fig.  404).     "  From  the  earliest  settlement  of  America  the  cod 


Fig.  404.  —  The  cod,  Gadus  callarias.     (From  the  Cambridge  Natural 
History,  after  Goode.) 


has  been  the  most  valuable  of  our  Atlantic  coast  fishes.     In- 
deed, the  codfish  of  the  Banks  of  Newfoundland  was  one  of  the 


CLASS  PISCES  471 

principal  inducements  which  led  England  to  establish  colonies  in 
America."  (Jordan  and  Evermann.)  The  total  weight  of  the 
codfishes  landed  at  Boston  and  Gloucester  in  1908  was  41,615,- 
277  pounds,  valued  at  $1,042,683.  The  Bureau  of  Fisheries 
distributes  millions  of  fry  every  year  (see  Table  XV). 

Subclass  II.  Dipnoi.  The  Lt?ng-fishes.  —  The  lung-fishes, 
of  which  there  are  only  three  living  genera,  are  said  to  be  inter- 
mediate between  the  fishes  and  amphibians.  They  possess 
certain  structural  features  not  found  in  other  fishes,  but  char- 
acteristic of  Amphibia.  On  the  other  hand,  they  are  in  many 
respects  like  the  Holocephali  and  Crossopterygii.  Among 
their  important  characters  are  their  -acutely  lobate,  paired  fins 
(Fig.  405),  an  opening  between  the  nasal  sac  and  the  mouth 
cavity,  a  peristent,  unconstricted  notochord,  and  an  air-bladder 
which  opens  into  the  pharynx  and  functions  as  a  lung. 

Family  Ceratodontid^.  — The  AustraUan  lung-fish,  Neocera- 
todus  fosteri  (Fig.  405),  is  the  only  Uving  species  belonging  to  this 


Fig.  405.  —  The  Australian  lung-fish,  Neoceratodus  fosteri.     (From  Sedg- 
wick's Zoology,  after  Giinther.) 

family.  It  lies  on  the  bottom  of  stagnant  pools  and  feeds  on 
worms,  moUusks,  crustaceans,  and  other  small  animals  that  it 
gathers  from  the  vegetation.  Occasionally  it  comes  to  the  sur- 
face in  order  to  change  the  air  in  its  single  lung.  Because  of 
this  lung  it  can  exist  in  water  unfit  for  fishes  that  breathe 
entirely  with  gills.  Such  an  environment  may  have  led  to 
the  evolution  of  lung-breathing  Amphibia  from  gill-breathing 
fishes. 

Family  Lepidosirenid^.  —  This  family  contains  two  genera 
of  living  fish.     The  three  species  of  the  genus  Protopterus  (Fig. 


472 


COLLEGE  ZOOLOGY 


406)  are  found  in  the  marshes  of  Central  Africa.  They  feed  on 
crustaceans,  worms,  insects,  and  frogs,  and  breathe  with  a  pair 
of  lungs.     During  the  dry  summer  season  they  burrow  about 


Fig.  406. 


The  African  lung-^sh,' Protopterus  anneciens. 
Zoology,  after  Claus.) 


(From  Sedgwick's 


eighteen  inches  into  the  mud,  where  a  cocoon  of  slime  is  secreted, 
and  the  fish  remains  inactive,  breathing  with  its  lungs,  and 
living  on  fat  stored  in  the  kidneys  and  gonads,  until  the  rainy 
season  comes  again. 

The  second  genus  of  this  family,  Lepidosiren,  has  but  a  single 
species,  Lepidosiren  paradoxa  (Fig.  407),  confined  to  the  marshes 
and  swamps  of   South  America.     It   feeds  on  algae,  mollusks. 


Fig.  407. 


-  The  South  American  lung-fish,  Lepidosiren  paradoxa. 
(From  Shipley  and  MacBride,  after  Kerr.) 


and  other  plants  and  animals,  and  comes  to  the  surface  to  change 
the  air  in  its  lungs.  Like  the  African  lung- fish,  it  hibernates  in 
the  mud  during  the  dry  season. 


5.   Deep-sea  Fishes 

Many  families  of  fishes  contain  deep-sea  species,  and  about 
thirty  families  of  teleosts  are  known  only  from  specimens  taken 
in  the  sea  at  depths  of  over  a  thousand  fathoms.  At  this  depth 
conditions  are  quite  different  from  those  near  the  surface. 
There  is  probably  no  sunlight  below  two  hundred  fathoms;  the 


CLASS  PISCES 


473 


temperature  is  always  a  few  degrees  above  the  freezing-point; 
the  pressure  is  a  ton  or  more  to  the  square  inch,  whereas  it  is 
only  about  fifteen  pounds  at  the  surface;  and  there  is  no  vege- 
tation, so  that  the  inhabitants  of  the  depths  must  be  carnivorous 
or  live  on  organisms  that  sink  toward  the  bottom. 

Fishes  meet  these  conditions  ift  various  ways  and  are  often 
curiously  modified.     Some  have  very  large  eyes  so  as  to  catch 


Fig.  408. 


A  deep-sea  fish,  Stomias  boa.     The  white  dots  are  the  luminous 
organs.     (From  Parker  and  Haswell,  after  Filhol.) 


as  many  rays  of  light  as  possible;  these  eyes  probably  serve  in 
connection  with  phosphorescent  organs.  Others  have  small  or 
rudimentary  eyes  and  are  blind;  they  depend  upon  tactile  organs 
instead  of  eyes.  Many  have  large  mouths  with  long,  sharp  teeth, 
and  enormous  stomachs.  The  phosphorescent  organs  are  vari- 
ously distributed  over  the  body  (small  circular  areas  in  Fig. 
408).  Some  of  them  consist  of  a  cup  of  secretory  cells  covered 
by  a  cellular  lens.  The  secretion  is  luminous,  and  in  certain  cases 
acts  as  a  lure;  in  others  it  probably  enables  the  fish  to  see  in 
the  dark  abyss  of  the  ocean. 


474  COLLEGE  ZOOLOGY 

6.  Fossil  Fishes 

A  large  number  of  species  of  fish  are  known  only  from  their 
fossil  remains.  The  earliest  fish  remains  consist  of  spines  and 
scales  from  the  lower  Silurian  or  Ordovician  strata  of  the  earth's 
crust,  which  were  laid  down  probably  twenty- five  million  years 
ago  (see  Table  XVII).  The  slightly  younger  Devonian  age 
is  called  the  ''  Age  of  Fishes  "  because  of  the  predominance  of 
fishes  over  the  other  animals  that  Uved  at  that  time.  A  con- 
siderable portion  of  the  Teleostomi  are  fossils;  four  of  the 
five  families  of  the  Crossopterygii;  five  of  the  seven  families 
of  the  Chondrostei;  six  of  the  eight  famiUes  of  the  Holostei; 
and  about  fifteen  families  of  the  Teleostei  are  fossil  forms. 
In  the  Dipnoi  there  are  two  families  of  fossil  and  two  of  living 
species.  The  study  of  fossil  fishes  is  very  important  because  of 
the  light  these  prehistoric  forms  shed  upon  the  affinities  of 
modern  species. 

7.  The  Economic  Importance  of  Fishes 

Fishes  furnish  an  important  article  of  food  for  man,  and  many 
of  them  provide  a  means  of  recreation  because  of  the  difficulty 
of  hooking  them  and  the  desperate  struggles  they  make  before 
they  can  be  captured.  Most  game-fishes  are  also  useful  as  food, 
but  this  is  not  always  the  case;  for  example,  the  tarpon  which 
occurs  on  our  Atlantic  coast  is  the  greatest  of  game-fishes,  but 
is  not  ordinarily  eaten  by  man.  A  few  species  are  injurious  be- 
cause  of  the  number  of  food-fishes  and  other  valuable  animals 
they  destroy. 

The  value  of  the  fishing  industry  may  be  judged  from  sta- 
tistics obtained  at  Boston  and  Gloucester,  where  about  seven 
eighths  of  all  the  fish  captured  offshore  along  the  Atlantic  coast 
are  brought  by  the  fishermen.  During  the  calendar  year  1908, 
181,465,000  pounds  of  fish,  worth  to  the  fishermen  $4,629,000, 
were  landed  at  these  two  cities.     The  most  important  species 


CLASS  PISCES  475 

were  the  cod,  haddock,  hake,  pollock,  halibut,  and  mackerel. 
The  salmon  fisheries  of  Alaska  are  even  more  valuable.  The 
total  quantity  taken  in  1908  was  198,952,814  pounds,  valued 
at  $10,683,051.  Fifty  canneries  and  forty  salting  estabUsh- 
ments  were  operated,  and  12,183  persons  were  employed  to  catch, 
prepare,  and  transport  the  canned,  pickled,  fresh,  and  frozen 
fish. 

Of  the  fresh-water  fishes  the  whitefish,  lake-trout,  rainbow- 
trout,  brook  trout,  catfishes,  sturgeon,  suckers,  black  bass,  pike, 
and  perch  are  some  of  the  more  important  species. 

In  many  places  the  fishes  have  been  captured  in  such  great 
numbers  that  laws  regulating  the  fishing  industry  have  been 
passed.  The  federal  and  state  governments  have  also  for  many 
years  operated  fish  hatcheries  where  the  eggs  of  important 
fishes  are  kept  during  their  development.  In  nature  very  few 
eggs  are  allowed  to  develop  because  of  the  attacks  of  fimgi,  and 
of  animals  such  as  other  fishes,  crayfishes,  and  wild  fowls.  A 
large  percentage  of  the  eggs  collected  and  cared  for  in  fish 
hatcheries  develop.  They  are  distributed  either  as  well-de- 
veloped eggs  or  as  yoimg  fish,  and  are  planted  in  the  waters  from 
which  the  adult  fishes  were  taken,  and  also  in  waters  where  the 
fishes  are  not  native. 

In  1909  the  Bureau  of  Fisheries  operated  35  hatcheries  and  84 
subhatcheries,  auxiliaries,  and  egg-collecting  stations ;  these  were 
located  in  32  states  and  territories.  "  The  regular  hatcheries 
may  be  classified  as  follows  with  reference  to  the  fishes  propa- 
gated: Marine  species,  3;  river  fishes  of  the  eastern  seaboard,  5; 
fishes  of  the  Pacific  coast,  5 ;  fishes  of  the  Great  Lakes,  7 ;  fishes 
of  the  interior  regions,  15."  (Bowers.)  The  total  output  of 
fish  and  eggs  in  1909  was  3,107,131,911.  "During  the  year 
applications  were  received  for  fish  for  planting  in  10,111  dif- 
ferent bodies  of  water."  A  summary  of  distributions  is  given  in 
Table  XV. 


476 


COLLEGE  ZOOLOGY 
TABLE  XV 


SOME   OF   THE   FISH  AND   EGGS  DISTRIBUTED   BY   U.S.    BUREAU   OF 
FISHERIES  FROM  JUNE  30,    I908,   TO  JUNE   30,    1909 


Species 

Eggs 

FryI 

FiNGERLINGS  2 

Total 

I.   Flatfish 

786,626,000 

786,626,000 

2.  Pike-perch 

457,850,000 

187,050,000 

644,900,000 

3.  Whitefish 

142,220,000 

277,445,000 

419,665,000 

4.  White  perch 

24,500,000 

318,760,000 

2,650 

343,262,650 

5.  Yellow  perch 

10,000,000 

213,610,410 

50,873 

223,661,283 

6.   Cod 

153,536,000 

153,536,000 

7.  Blueback 

salmon 

100,000 

93,409,496 

93,509,496 

8.  Lake-trout 

22,806,000 

27,188,177, 

1,345,100 

51,339,277 

9.  Brook  trout 

905,000 

5,821,322 

3,723,489 

10,449,811 

10.  Rainbow- trout 

286,150 

292,408 

2,026,463 

2,605,021 

II.  Large-mouth 

black  bass 

32,500 

540,962 

573,462 

12.  Small-mouth 

black  bass 

262,674 

111,924 

374,598 

Besides  this,  568,150  eggs  were  shipped  to  Argentina,  France, 
and  Germany. 

The  destructive  fishes  are  injurious  principally  because  they 
devour  other  valuable  fish,  lobsters,  etc.  Of  the  fresh-water 
fishes  belonging  in  this  category  may  be  mentioned  the  bowfin, 
Amia  calva  (Fig.  384),  which  bites  voraciously  and  breaks  tackle; 
the  garpike,  Lepisosteus  osseus  (Fig.  383),  which  is  very  de- 
structive to  young  fish;  the  German  carp,  Cyprinus  carpio 
(Fig.  386),  which  stirs  up  mud  and  keeps  out  superior  fish;  and 
the  muskallunge,  Esox  masguinongy,  which  does  considerable 
damage  by  devouring  the  young  of  whitefish  and  other  food- 
fishes. 

1  Fry  =  fish  up  to  the  time  the  yolk  sac  is  absorbed  and  feeding  begins. 

2  Fingerlings  =  fish  between  the  length  of  one  inch  and  the  yearling  stage. 


CHAPTElt    XVIII 
SUBPHYLUM    VERTEBRATA:     CLASS    IV.     AMPHIBIA 

The  common  amphibians  are  the  frogs,  toads,  and  salamanders. 
They  spend  part  or  all  of  their  existence  in  the  water  or  in 
damp  places.  Most  of  them  lay  their  eggs  in  the  water,  and 
the  larvae,  which  breathe  with  gills,  are  known  as  tadpoles  or 
poUywogs.  Some  amphibians  are  often  confused  with  reptiles 
(especially  with  the  lizards)  because  of  their  similarity  of  form, 
but  almost  all  reptiles  possess  scales,  whereas  amphibians  have 
UiiUtllly  a  ?im00th,  ?i\\my  fikin  without.  SCalfifi  except  in  a  few  rare 
species.  There  are  two  orders  of  extinct  amphibia  and  three 
orders  of  hving  forms.     The  latter  are  as  follows:  — 

Order  i.  Apoda. — The  Apoda  or  Cgecilians  are  legless, 
worm-like  amphibians  inhabiting  tropical  and  subtropical 
regions. 

Order  2.  Caudata.  — These  are  amphibians  with  tails.  They 
include  the  mud-puppies,  sirens,  and  salamanders. 

Order  3.  Salientia.  —  The  tailless  Amphibia,  frogs  and 
toads,  belong  to  this  order. 

I.  The  Frog 

The  leopard  frog,  Rana  pipiens,  lives  in  or  near  fresh-water 
lakes,  ponds,  and  streams,  and  is  distributed  over  the  North 
American  continent  except  on  the  Pacific -slope.  The  frog  leaps 
on  land  and  swims  in  the  water.  The  hind  legs  are  large  and 
powerful.  When  the  frog  is  on  land  they  are  folded  up,  and 
a  sudden  extension  propels  the  body  through  the  air.  Like- 
wise in  swimming  the  hind  legs  are  alternately  folded  up  and 
(    1  477 


478  COLLEGE  ZOOLOGY 

extended,  and  during  their  backward  stroke  the  toes  are  spread 
apart  so  as  to  offer  more  resistance  to  the  water.  Frequently 
frogs  float  on  the  surface  with  just  the  tip  of  the  nose  exposed 
and  with  the  hind  legs  hanging  down.  When  disturbed  in  this 
position,  the  hind  legs  are  flexed,  a  movement  which  withdraws 
the  body,  the  fore  legs  direct  the  frog  downward,  and  then  the 
hind  legs  are  extended,  completing  the  dive. 

Frogs  croak  mostly  during  the  breeding  season,  but  also  at 
other  times  of  the  year,  especially  in  the  evening  or  when  the 
atmosphere  becomes  damp.  Croaking  may  take  place  either 
in  air  or  under  water.  In  the  latter  case  the  air  is  forced  from 
the  lungs,  past  the  vocal  cords,  into  the  mouth  cavity,  and  back 
again. 

The  principal  enemies  of  frogs  are  snakes,  turtles,  cranes, 
herons,  other  Amphibia,  and  man.  The  excellence  of  frogs'  legs 
for  the  table  has  resulted  in  widespread  destruction,  and  this 
has  been  augmented  by  the  capture  of  great  numbers  for  use 
in  scientific  investigations.  Tadpoles  faU  a  prey  to  aquatic 
insects,  fishes,  and  water-fowl,  and  very  few  of  them  reach 
maturity. 

External  Features.  —  The  body  of  the  frog  may  be  divided 
into  the  head  and  trunk.  The  eyes  usually  protrude  from  the 
head,  but  are  drawn  into  their  orbits  when  the  frog  closes  its  eye- 
lids. Behind  each  eye  is  a  tympanic  membrane  covering  the  ear- 
drum. A  pair  of  nostrils  or  external  nares  are  situated  on  the 
dorsal  surface  near  the  end  of  the  snout.  Just  in  front  of  the 
eyes  in  some  specimens  is  a  light  area,  called  the  brow  spot, 
which,  in  the  embryo,  was  connected  with  the  brain.  The  mouth 
of  the  frog  extends  from  one  side  of  the  head  to  the  other.  The 
anus  is  situated  at  the  posterior  end  of  the  body. 

The  fore  legs  are  short  and  serve  to  hold  up  the  anterior  part 
of  the  body.  The  hands  possess  four  digits  and  the  rudiment 
of  a  fifth,  the  thumb.  In  the  male  the  inner  digit  is  thicker  than 
the  corresponding  digit  of  the  female,  especially  during  the  breed- 
ing season.     The  hind  legs  are  folded  together  when  the  frog  is 


CLASS   AMPHIBIA 


479 


at  rest.  They  are  long  and  powerful.  The  five  toes  are  con- 
nected by  a  web,  making  the  foot  an  efficient  swimming  organ. 
The  skin  is  smooth  and  loose;  it  contains  large  black  pigment 
spots  and  a  lesser  amount  of  green  and  golden  pigments.  The 
skin  consists,  as  in  other  vertebrates  (Fig.  347),  of  two  layers,  an 
outer  epidermis  and  an  inner  dermts.  It  is  furnished  with  a  large 
number  of  mucus  glands  which  secrete  the  fluid  that  makes  the 


^C 


surface  of  the  body 

sHmy,  and  a  smaller 

number    of     poison 

glands,  which  secrete 

a  whitish  fluid  of  use    ,/  ,/  >-^;^^>\'>-5li>::>i^^  \ 

probably  for  defen-  U   i^^^V'-^-?"^::^?^^^ 


sive  purposes 

General     Internal 
Anatomy.  —  The 

body  of  the  frog  is 
supported  by  a  bony 
skeleton,  is  moved 
by  muscles,  and 
contains  a  well-de- 
veloped nervous 
system.  If  the  body- 
wall  is  slit  open  in 
the  ventral  middle 
line  from  the  pos- 
terior   end    of    the 


Fig.  409.  —  Diagrammatic  transverse  section  of 
the  body  of  a  female  frog,  to  show  relation  of  peri- 
toneum (broken  line)  to  viscera.  Ao,  aorta; 
Ds,  dorsal  subcutaneous  lymph  space;  G,  intestine; 
IV C,  inferior  vena  cava;  K,  kidney;  LS,  lateral 
subcutaneous  lymph  space;  NC,  spinal  cord; 
n,  n,  nerves;  Od,  oviduct;  Ov,  ovary;  S,  great  dorsal 
lymph  space;  V,  vertebral  centrum;  VS,  ventral 
subcutaneous  lymph  space;  i,  2,  3,  mesenteries  sus- 
pending the  intestine,  ovaries,  and  oviducts.  The 
skin  is  represented  by  a  thick  black  line.  (From 
Bourne.) 


body   to    the    angle 

of  the  jaw,  the  organs  in  the  body-cavity  or  coslom  will  be 

exposed. 

The  heart  lies  within  the  sac-like  pericardium;  it  is  partially 
surrounded  by  the  three  lobes  of  the  reddish  brown  liver.  The 
two  lungs  lie  one  on  either  side  near  the  anterior  end  of  the  ab- 
dominal cavity.  Coiled  about  within  the  body-cavity  are  the 
stomach  and  intestine.    The  kidneys  are   flat  reddish  bodies 


48o 


COLLEGE  ZOOLOGY 


attached  to  the  dorsal  body-wall  The  two  testes  of  the  male 
are  small  ovoid  organs  suspended  by  membranes  and  lying  at 
the  sides  of  the  alimentary  canal.  The  ovaries  and  oviducts  of 
the  female  occupy  a  large  part  of  the  body-cavity  during  the 
breeding  season.  The  ccelom  is  lined  with  a  mesodermal  mem- 
brane, the  peritoneum  (Fig.  409).  The  reproductive  organs 
and  alimentary  canal  are  suspended  by 
double  layers  of  peritoneum  called  mesen- 
teries (Fig.  409,  I,  2,  j). 

The  Digestive  System.  —  The  food  of 
the  frog  consists  principally  of  living  worms 
and  insects.  These  are  usually  captured 
by  the  extensile  tongue,  which  can  be  thrown 
forward  as  shown  in  Figure  410.  The  object 
adheres  to  the  tongue,  which  is  covered  with//' 
a  sticky  secretion,  and  is  then  drawn  into 
the  mouth.  No  attention  is  paid  to  objects 
that  are  not  moving.  Large  insects  are 
pushed  into  the  mouth  with  the  forefeet. 
If  the  object  swallowed  is  undesirable,  it 
can  be  ejected  through  the  mouth. 
The  mouth  cavity  is  large  (Fig.  411).     The 

Ranaesculenia     {From    ^^^^^^    (7^)    Jigg   ^^   ^^e    floor   of   the   Cavity 
the  Cambridge  Natural        .        . 

History.)  With  its  anterior  end  attached  to  the  jaw 

and  its  forked  posterior  end  lying  free. 
When  a  lymph  space  beneath  the  tongue  is  filled,  the  tongue 
is  thrown  forward  for  capturing  insects  (Fig.  410).  The  teeth 
are  conical  in  shape  and  are  borne  by  the  upper  jaw  and  by 
two  bones  of  the  roof  of  the  mouth  called  vomers  (Fig.  411,  V). 
They  are  used  only  for  holding  food  and  not  for  masticating  it. 
New  teeth  replace  those  that  become  worn  out. 

The  oesophagus  opens  into  the  mouth  cavity  by  a  horizontal 
slit  (Fig.  411,  O);  it  is  a  short  distensible  tube  leading  directly 
to  the  stomach.  The  stomach  is  crescent-shaped  and  lies  mostly 
on  the  left  side  of  the  body;  it  is  large  at  the  anterior  or  cardiac 


Fig.  410.  —  Three 
stages  of  the  movement 
of  the  tongue  of  a  frog, 


CLASS   AMPHIBIA 


481 


end,  but  constricted  at  the  posterior  or  pyloric  end  where  it  joins 
the  small  intestine.  The  walls  of  the  stomach  are  thick,  con- 
sisting of  four  layers  :  (i)  the  outer  thin  peritoneum ;  (2)  a  tough 
muscular  layer ;  (3)  a  spongy  layer,  the  suhmucosa;  and  (4)  an 
inner  folded  mucous  layer,  the  mucosa.  The  mucosa  is  made 
up  oi' glands  lying  in  connective* tissue. 
Near  the  cardiac  end  the  glands  are 
longer  than  at  the  pyloric  end. 

The  anterior  portion  of  the  small  in- 
testine is  known  as  the  duodenum;  this 
leads  to  the  much-coiled  ileum,  which 
widens  into  the  large  intestine.  The  ali- 
mentary canal,  as  well  as  the  urinary 
bladder  and  reproductive  ducts,  open 
into  a  sac-like  cavity  called  the  cloaca. 
The  inner  layer  of  the  intestine,  the 
mucosa,  is  much  folded ;  it  consists  of 
ordinary  absorptive  cells  and  goblet 
cells. 

The  digestive  glands  are  the  pancreas 
and  liver.  The  pancreas  lies  between 
the  duodenum  and  the  stomach.  It  is 
a  much-branched  tubular  gland  which 
secretes  an  alkaline  digestive  fluid  and 
empties  it  into  the  common  bile-duct. 

rryy       j-         •  i  ,v  ii^j        jj'T.     vomcr  ,*  tp,  tubcrculum  pre- 

The  hver  is  a  large  three-lobed  reddish  Unguale.  (From  Holmes.) 
gland  which  secretes  an  alkaline  diges- 
tive fluid  called  bile.  This  fluid  is  carried  by  bile  capillaries 
into  the  gall-bladder,  where  it  is  stored  until  food  enters  the  in- 
testine, when  it  passes  into  the  duodenum  through  the  common 
bile-duct. 

Digestion  begins  in  the  stomach.     The  alkaline  fluid  secreted 

by  the  mucosa  layer  of  the  oesophagus  and  the  acid  gastric  juice 

secreted  by  the  glandular  walls  of  the  stomach  digest  out  the 

proteid  portion  of  the  food  by  means  of  sl  ferment,  called  pepsin  ^ 

2  I 


Fig.  411.  —  Mouth  of 
the  frog  widely  opened. 
E,  Eustachian  tubes; 
G,  glottis;  /,  lower  jaw; 
L,  lateral  subrostral  fossa ; 
M,  median  subrostral 
fossa;  N,  posterior  nares; 
O,  oesophagus;  F,  pulvinar 
rostrale ;  S,  opening  of 
vocal  sac ;   T,  tongue ;  V, 


482  COLLEGE  ZOOLOGY 

which  changes  proteids  into  soluble  peptones.  The  food  then 
•passes  thcough  the  pyloric  constriction  into  the  intestine.  Here 
it  is  attacked  by  the  pancreatic  juice  and  the  bile.  The  pan- 
creatic juice  contains  three  ferments:  (i)  trypsin,  which  converts 
proteids  into  peptones;  (2)  amylopsin,  which  converts  starch  into 
sugar;  and  (3)  steapsin,  which  splits  up  fats  into  fatty  acid  and 
glycerin.  The  bile  emulsifies  fats  and  converts  starch  into  sugar. 
The  intestinal  wall  produces  a  secretion  which  probably  aids  in 
converting  starch  into  sugar. 

Absorption  begins  in  the  stomach,  but  takes  place  principally 
in  the  intestine.  The  food  substances  which  have  been  dis- 
solved by  the  digestive  juices  are  taken  up  by  the  mucosa  layer, 
passed  into  the  blood  and  lymph,  and  are  then  transported  to 
various  parts  of  the  body.  The  undigested  particles  of  food 
pass  out  of  the  intestine  into  the  cloaca  and  are  then  discharged 
through  the  anus  as  faeces. 

The  absorbed  food  is  used  by  the  frog  to  build  up  new  pro- 
toplasm to  take  the  place  of  that  consumed  in  the  various  life 
activities,  and  to  increase  the  size  of  the  body.  Food  is  stored 
up  in  the  liver  as  glycogen,  a  carbohydrate  similar  to  starch  and 
often  called  "  animal  starch."  When  needed  by  the  body,  this 
glycogen  is  changed  into  dextrose  by  enzymes  produced  by  the 
liver,  and  slowly  passed  into  the  blood.  During  the  winter 
the  hibernating  frog  lives  largely  on  the  glycogen  stored  up  in 
the  liver  in  the  autumn.  „ 

The  Respiratory  System.  — '  Respiration  takes  place  to  a  con- 
siderable extent  through  the  skin  both  in  water  and  in  air,  but 
is  carried  on  principally  by  the  lungs.  As  shown  in  Figure  412, 
air  passes  through  the  nostrils  or  external  nares  (Fig.  412,  A,  e.n) 
into  the  olfactory  chamber  (olf.s),  and  then  through  the  internal 
or  posterior  nares  (Fig.  412,  i.n;  Fig.  411,  N)  into  the  mouth 
cavity.  The  external  nares  are  then  closed  (Fig.  412,  B,  e.n), 
the  floor  of  the  mouth  is  raised,  and  the  air  is  forced  through  the 
glottis  (Fig.  412,  B,  gl;  Fig.  411,  G)  into  a  short  tube,  the  larynx, 
and  thence  into  the  lungs  (Ing).    Air  is  expelled  from  the  lungs 


CLASS  AMPHIBIA 


483 


into  the  mouth  cavity  by  the  contraction  of  the  muscles  of  the 
body-wall. 

The  air  in  the  mouth  cavity  is  changed  by  throat  movements. 
The  glottis  remains  closed,  while  the  floor  of  the  mouth  is  alter- 


pm> 


^uZ 


Fig.  412.  —  Diagram  to  illustrate  the  respiratory  movements  of  the  frog. 
In  A  the  floor  of  the  mouth  is  depressed,  the  nares  are  open,  and  air  rushes 
through  them  into  the  buccal  cavity.  In  B,  the  floor  of  the  mouth  is  raised, 
the  nares  are  closed,  and  air  is  forced  from  the  buccal  cavity  into  the  lungs. 
e.n,  external  nares ;  gl,  glottis ;  gid,  gullet ;  i.n,  internal  nares ;  Ing,  lung ; 
0IJ.S,  olfactory  chamber ;  pmx,  premaxillary  bone ;  tng,  tongue.  (From  Holmes, 
after  Parker.) 


nately  raised  and  lowered.  Air  is  thus  drawn  in  and  expelled 
through  the  nares. 

Tne  lungs  are  pear-shaped  sacs  with  thin,  elastic  walls.  The 
area  of  their  inner  surface  is  increased  by  folds  which  form 
minute  chambers  called  alveoli.  Blood  capillaries  are  numerous 
in  the  walls  of  these  alveoli. 

The  larynx  is  strengthened  by  five  cartilages.  Across  it  are 
stretched  two  elastic  bands,  the  weal  cords.  The  croaking  of 
the  frog  is  produced  by  the  vibrations  of  the  free  edges  of  the 


484 


COLLEGE  ZOOLOGY 


vocal  cords  due  to  the  expulsion  of  air  from  the  lungs.  The 
laryngeal  muscles  regulate  the  tension  of  the  cords,  and  hence  the 
pitch  of  the  sound.  Many  male  frogs  have  a  pair  of  vocal  sacs 
which  open  into  the  mouth  cavity  (Fig.  411,  S)]  they  serve  as 
resonators  to  increase  the  volume  of  sound. 

The  Circulatory  System.  —  The  circulatory  system  of  the 
frog  consists  of  a  heart,  arteries,  veins,  and  lymph  spaces.  The 
hlood  is  a  plasma  containing  three  kinds  of  corpuscles,  —  red 
corpuscles,  white  corpuscles,  and  spindly  cells.  The  blood 
plasma  carries  food  and  waste  matter  in  solution.  It  coagu- 
lates under  certain  conditions,  forming  a  clot  of  fibrin  and  cor- 
puscles, and  a  liquid  called  serum.     The  power  of  coagulation 

is  of  decided  benefit, 
v-;?-?^'*'-*^  .rr^h.      since    the    clot   soon 

closes  a  wound  and 
thus  prevents  loss  of 
blood. 

The  red  corpuscles 

Fig.  413  a.  —  Blood-  corpuscles  of  the  frog,  (erythrocytes,  Fig. 
a   red;  b,  white;  c,  spindle  cells.     (From  Holmes,  \  elliptical, 

after  Dekhuyzen.)  t  o  .  j     /       ^         f  j 

flattened  cells  con- 
taining a  substance  called  hcemoglobin.  Haemoglobin  combines 
with  oxygen  in  the  capillaries  of  the  respiratory  organs  and 
gives  it  out  to  the  tissues  of  the  body.  The  white  corpuscles 
(leucocytes,  Fig.  413  a,  b)  are  ameboid  in  shape,  vary  in  size, 
and  are  capable  of  independent  movement.  They  are  of 
great  value  to  the  animal,  since  they  engulf  small  bodies,  such 
as  bacteria,  thereby  frequently  preventing  the  multiplication 
of  pathogenic  organisms  and  consequently  helping  to  overcome 
germ  diseases.  White  corpuscles  also  aid  in  the  removal  of 
broken-down  tissue.  The  spindle  cells  (Fig.  413  a,  c)  are  usually 
spindle-shaped.  In  the  springtime  they  develop  into  red  cor- 
puscles. Blood  corpuscles  arise  principally  in  the  marrow  of 
the  bones.  They  also  increase  in  numbers  by  division  while 
in  the  blood-vessels.     Some  white  corpuscles  are  probably  formed 


CLASS   AMPHIBIA 


485 


in  the  spleen,  a  gland  in  which  worn-out  red  corpuscles  are 
destroyed. 

The  heart  (Fig.  413  b,  Fig.  414)  is  the  central  pumping  station 
of  the  circulatory  system.  It  is  composed  of  a  conical,  muscular 
ventricle  (Fig.  413  b,  /),  two  thin- walled  auricles,  one  on  the  right 
{2),  the  other  on  the  left  (j),  a  tHick- walled  tube,  the  truncus 
arteriosus  {4) ,  which  arises  from  the  base  of  the  ventricle,  and  a 


—13 


Fig.  413  b.  —  Heart  of  the  frog.  A,  ventral  view.  B,  dorsal  view.  C,  ven- 
tral wall  removed.  /,  ventricle;  2,  right  auricle,  3,  left  auricle;  4,  truncus; 
arteriosus;  5,  carotid  arch;  6,  lingual  artery;  7,  carotid  gland;  8,  carotid 
artery;  p,  systemic  arch;  10,  pulmocutaneous  arch;  11,  innominate  vein; 
12,  subclavian  vein;  13,  vena  cava  inferior;  14,  vena  cava  superior;  is,  opening 
of  sinus  venosus  into  right  auricle;  16,  pulmonary  vein;  17,  aperture  of  entry 
of  pulmonary  vein;  18,  semi-lunar  valves;  19,  longitudinal  valve;  20,  point  of 
origin  of  pulmocutaneous  arch.     (From  Shipley  and  MacBride,  after  Howes.) 


thin-walled,  triangular  sac,  the  sinus  venosus  (Fig.  413  b,  B),  on 
the  dorsal  side. 

The  arteries  (Fig.  414)  carry  blood  away  from  the  heart.  The 
truncus  arteriosus  (Fig.  413  b,  4;  Fig.  414,  tr.a)  divides  as  shown 
in  Figure  413,  A,  and  each  branch  gives  rise  to  three  arteries. 

(i)  The  common  carotid  (Fig.  413  b,  A,  5;  Fig.  414,  c.c)  divides 
into  the  lingual  or  external  carotid  (Fig.  414,  I),  which  supplies 
the  tongue  and  neighboring  parts,  and  the  internal  carotid,  which 
gives  off  the  palatine  artery  to  the  roof  of  the  mouth,  the  cerebral 


486 


COLLEGE  ZOOLOGY 


cu.- 


carotid  to  the  brain,  and  the  ophthalmic  artery  to  the  eye.  Where 
the  common  carotid  branches  is  a  swelUng  called  the  carotid 
gland  (Fig.  413  b,  A,  7);    this  body  impedes  the  blood  flow 

„  in   the    internal    carotid 

'^^^.  artery. 

C^oc  (2)  The  pulmocutaneous 

'  5^  artery  (Fig.  413  b,  A,  70; 
Fig.  414,  p.cu)  branches, 
forming  the  pulmonary 
artery,  which  passes  to 
the  lungs,  and  the  cutane- 
ous artery.  The  latter 
gives  off  the  auricularis, 
which  is  distributed  to 
the  lower  jaw  and  neigh- 
boring parts,  the  dorsalis, 
which  supplies  the  skin 
of  the  back,  and  the 
lateralis,  which  supplies 
the  skin  of  the  sides. 
Most  of  thesp  branches 
carry  blood  to  the  re- 
spiratory organs — lungs, 
skin,  and  mouth. 

(3)  The  third  branches 

Fig.  4i4--DiagramJrhe  arterial  system    ^^    ^>'^^^^^*^    ^J'^^'    ^^J; 
of  the  frog,   ventral  view,     ao",  aortic  arch;     413  b, A, QJ   Fig.  414,^0    ) 

after  passing  outward 
and  around  the  aliment- 
ary canal  unite  to  form 
the  dorsal  aorta  {d.ao). 
As  shown  in  Figure  414, 
each  systemic  arch  gives 
off  an  occipito-vertebral 
artery,  which  divides,  one 


cm',  right  auricle;  aw",  left  auricle;  ftr,  brachial 
artery ;  c.c,  carotid ;  c.gl,  carotid  gland ; 
c.il,  common  iliac ;  cce,  cocliaco-mesenteric ; 
cm',  cceliac;  cu,  cutaneous;  d.ao,  dorsal  aorta; 
Jm,  femoral ;  g,  gastric ;  h,  hoemorrhoidal ; 
^/>,  hepatic;  Ay,  epigastrico-vesical;  ^.kidney; 
/,  lingual;  Ig",  left  lung;  m,  anterior  mesen- 
teric; m.i,  posterior  mesenteric;  oc,  occipital; 
pc',  pancreatic ;  p.cu,  pulmocutaneous ;  pul, 
pulmonary;  re,  renal;  sc,  sciatic;  5/>,  splenic; 
tr.a,  truncus  arteriosus;  ts,  testis;  v,  vertebral. 
(From  Holmes,  after  Howes.) 


CLASS  AMPHIBIA  487 

branch,  the  occipital  (oc),  supplying  the  jaws  and  nose,  the 
other,  the  vertebral  (v),  supplying  the  vertebral  column,  and  a 
subclavian  artery  (br),  which  is  distributed  to  the  shoulder, 
body- wall,  and  arm.  The  dorsal  aorta  (d.ao)  gives  off  the  coeh- 
aco-mesenteric  artery  (cce);  this  divides,  forming  the  cceliac 
(cce'),  which  supplies  the  stomach,  pancreas,  and  liver,  and  the 
anterior  mesenteric  (m),  which  is  distributed  to  the  intestine, 
spleen,  and  cloaca.  Posterior  to  the  origin  of  the  cceliaco- 
mesenteric,  the  dorsal  aorta  gives  off  four  to  six  urinogenital 
arteries  (re)  which  supply  the  kidneys  (k),  reproductive  organs 
(ts),  and  fat  bodies.  A  small  posterior  mesenteric  artery  (m.i) 
arises  near  the  posterior  end  of  the  dorsal  aorta  and  passes  to 
the  rectum,  and  in  the  female  to  the  uterus.  The  dorsal  aorta 
finally  divides  into  two  common  iliac  arteries  (cal),  which  are 
distributed  to  the  ventral  body-wall,  the  rectum,  bladder,  the 
anterior  part  of  the  thigh  (femoral  artery,  fm),  and  other  parts 
of  the  hind  limbs  (sciatic  artery,  sc). 

The  yeim  (Fig.  415)  return  blood  to  the  heart.  The  blood 
from  the  lungs  is  collected  in  the  pulmonary  veins  (put)  and 
poured  into  the  left  auricle  (/.  au) .  The  rest  of  the  venous  blood 
is  carried  to  the  sinus  venosus  (s.v)  by  three  large  trunks,  the 
two  anterior  venae  cavae  (pr.  cv)  and  the  posterior  vena  cava. 
The  anterior  venae  cavae  receive  blood  from  the  external  jugulars 
{ext.  ju)  which  collect  blood  from  the  tongue,  thyroid,  and 
neighboring  parts,  the  innominates  which  collect  blood  from 
the  head  by  means  of  the  internal  jugulars  (int.  ju)  and  from 
the  shoulder  by  means  of  the  subscapulars,  and  the  subclavians 
which  collect  blood  from  the  fore  limbs  by  means  of  the 
brachial  (br)  and  from  the  side  of  the  body  and  head  by  means 
of  the  musculocutaneous  veins  (ms.  cu).  The  j^osteiior^_vena^ 
cava  receives  blood  from  the  liver  (Ivr)  by  means  of  two  hepatic 
veins  (hp),  from  the  kidneys  (kd)  by  means  of  four  to  six  pairs 
of  renal  veins  (rn) ,  and  from  the  reproductive  organs  (ts)  by 
means  of  spermatic  or  ovarian  veins. 

The  veins  which  carry  blood  to  the  kidneys  constitute  the 


488 


COLLEGE  ZOOLOGY 


jfm 


Fig.  415.  —  Diagram  of  the  venous  system  of  the  frog,  dorsal  aspect. 
ahd,  abdominal  vein;  hr,  brachial  vein;  cd,,  cardiac  vein;  ds.lmb,  dorso-lumbar 
vein;  du,  duodenal;  ext.ju,  external  jugular;  fm,  femoral;  gs,  gastric; 
hp,  hepatic;  hp.pt,  hepatic  portal;  int,  intestinal;  int.ju,  internal  jugular 
vein;  kd,  kidney;  l.au,  left  auricle;  Ing,  lung;  hr,  liver;  ms.cu,  musculocu- 
taneous vein;  pr.cv,  precaval;  pt.cv,  postcaval;  pul,  pulmonary;  pv,  pelvic; 
r.au,  right  auricle;  rn,  renal;  rn.pt,  renal  portal;  sc,  sciatic;  spl,  splenic; 
spm,  spermatic;  s.v,  sinus  venosus;  ts,  testis;  ves,  vesical  veins.  (From 
Parker  and  Haswell.) 


CLASS  AMPHIBIA  489 

renal  portal  system.  The  renal  portal  vein  (Fig.  415,  rn.pt) 
receives  the  blood  from  the  hind  legs  by  means  of  the  sciatic 
(sc)  and  femoral  {fm)  veins,  and  blood  from  the  body-wall  by 
means  of  the  dorso-lumbar  vein  (ds.hnb). 

The  liver  receives  blood  from  the  hepatic  portal  system.  The 
femoral  veins  (fm)  from  the  hind  limbs  divide,  and  their  branches 
unite  to  form  the  abdominal  vein  (abd).  The  abdominal  vein 
also  collects  blood  from  the  bladder,  ventral  body-wall,  and 
heart.  The  portal  vein  carries  blood  into  the  liver  from  the 
stomach,  intestine,  spleen,  and  pancreas. 

Circulation  takes  place  in  the  following  manner:  The  sinus 
venosus  contracts  first,  forcing  the  impure  venous  blood  into 
the  right  auricle  (Fig.  413  b,  C,  15).  Then  both  auricles  contract, 
and  the  oxygenated  blood  brought  into  the  left  auricle  by  the 
pulmonary  veins  is  forced  into  the  left  part  of  the  ventricle, 
and  the  impure  blood  from  the  right  auricle  is  forced  into  the 
right  side  of  the  ventricle.  The  ventricle  then  contracts  and 
the  impure  blood  is  forced  out  first,  passing  principally  into  the 
pulmocutaneous  arteries  and  thence  to  the  lungs  and  skin,  and 
the  oxygenated  blood  is  forced  out  later  through  the  carotid 
and  systemic  arteries  to  the  other  parts  of  the  body.  The  blood 
is  prevented  from  flowing  back,  and  the  oxygenated  blood  and 
impure  blood  are  distributed  as  stated  above,  by  means  of  valves 
(Fig.  413  b,  C,  18,  ig). 

The  blood  that  is  thus  forced  through  the  arteries  makes  its 
way  into  tubular  blood-vessels  that  become  smaller  and  smaller 
until  the  extremely  narrow  capillaries  are  reached.  Here  food 
and  oxygen  are  delivered  to  the  tissues,  and  waste  products  are 
taken  up  from  the  tissues.  The  renal  portal  system  carries 
blood  to  the  kidneys,  where  urea  and  similar  impurities  are  taken 
out.  The  hepatic  portal  system  carries  blood  to  the  liver,  where 
bile  and  glycogen  are  formed.  The  blood  brought  to  the  lungs 
and  skin  is  oxygenated  and  then  carried  back  to  the  heart.  The 
passage  of  blood  through  the  capillaries  can  easily  be  observed 
in  the  web  of  the  frog's  foot  or  in  the  tail  of  the  tadpole. 


>fe» 


490 


COLLEGE  ZOOLOGY 


The  lymph  spaces  in  the  frog's  body  are  very  large.  They 
communicate  with  one  another  and  with  the  veins.  Fourjymph 
hearts,  two  near  the  third  vertebra  and  two  near  the  end  of  the 
vertebral  column,  force  the  lymph  by  pulsations  into  the  internal 
jugular  and  transverse  iliac  veins.  The  lymph  is  colorless  and 
contains  colorless  corpuscles. 

The  Excretory  System  (Fig.  416).  —  A  certain  amount  of  sub- 
stance resulting  from  the  breaking  down  of  living  matter  is 


A  B 

Fig.  416.  —  Urinogenital  organs  of  the  frog.  A,  male.  i,  fat  body; 
2,  mesentery;  3,  efferent  ducts  of  testis;  4,  ducts  of  seminal  vesicle;  5,  seminal 
vesicle;  6,  archinephric  duct;  7,  cloaca;  8,  orifice  of  ureter;  g,  proctodeum  ; 
10,  allantoic  bladder;   11,  rectum;    12,  kidney;    13,  testis;    14,  adrenal  body. 

B,  female.  /,  oesophagus;  2,  mouth  of  oviduct;  3,  left  lung;  4,  fat  body; 
5,  left  ovary;  6,  archinephric  duct;  7,  oviduct;  8,  allantoic  bladder;  g,  cloaca; 
10,  aperture  of  oviduct;  it,  aperture  of  archinephric  duct;  12,  proctodeum; 
13,  mesentery;  14,  kidney.     (From  Shipley  and  MacBride,  after  Howes.) 


excreted  by  the  skin,  liver,  and  intestinal  walls,  but  most  of  it 
is  taken  from  the  blood  in  the  kidneys  (Fig.  416,  A,  12),  passes 
through  the  ureters  (6),  and  then  by  way  of  the  cloaca  (7)  into 


CLASS   AMPHIBIA 


491 


the  bladder  (10),  where  it  is  stored  until  expelled  from  the  body 
through  the  anus.  The  kidney  is  composed  of  connective  tissue 
containing  a  large  number  of  uriniferous  tubules  (Fig.  417,  T), 
each  of  which  begins  in  a  Malpighian  body  (M),  consisting  of  a 
coiled  mass  of  blood-vessels,  the  glomerulus,  and  an  enclosing 
membrane  called  Bowman's  capstde.  The  excretions  are  carried 
by  the  uriniferous  tubules  to  a  collecting  tubule  (C)  and  thence 
into  the  ureter  {U).  Ciliated  funnels,  called  nephrostomes  (N), 
occur  in  the  ventral  portion;  these  are  in  the  young  frog  con- 
nected with  the  renal  tubules,  but  open  into  branches  of  the 


Fig.  417.  —  Diagram  of  a  cross-section  of  the  kidney  of  the  frog.  B,  Bidder's 
canal;  C,  collecting  tubule;  D,  dorsal  surface  of  kidney;  L,  lateral  edge  of 
kidney;  M,  Malpighian  body;  N,  nephrostome;  T,  uriniferous  tubules; 
U,  ureter;    V,  renal  portal  vein.     (From  Holmes.) 

renal  vein  in  the  adult.  Renal  arteries  (Fig.  414,  re)  and  the 
renal  portal  vein  (Fig.  415,  rn.pt;  Fig.  417,  F)  bring  blood  into 
the  kidney.  Blood  leaves  the  kidney  by  way  of  the  renal  veins 
(Fig.  415,  rn). 

The  Reproductive  System.  —  The  sexes  are  separate.  The 
male  can  be  distinguished  from  the  female  by  the  greater  thick- 
ness of  the  inner  digit  of  his  fore  legs.  The  spermatozoa  of  the 
male  arise  in  the  testes,  pass  through  the  vasa  eferentia  (Fig. 
416,  A,  j)  into  the  kidneys,  then  by  way  of  Bidder's  canal 
(Fig.  417,  B)  to  the  ureter  (Fig.  416,  A,  6);  and  thence  out 
through  the  anus. 

The  eggs  arise  in  the  ovaries  of  the  female  (Fig.  416,  B,  5), 
break  out  into  the  body-cavity,  make  their  way  into  the  coiled 


492 


COLLEGE  ZOOLOGY 


oviduct  {7)  through  a  small  opening  (2),  and  pass  down  into  the 
thin-walled,  distensible  uterus.  The  glandular  wall  of  the  ovi- 
duct secretes  the  gelatinous  coats  of  the  eggs.  The  fertilization 
and  development  of  the  eggs  will  be  described  later  (pp.  506- 

510). 

Just  in  front  of  each  reproductive  organ  is  a  yellowish,  glove- 
shaped /a^&(7f/3;  (Fig.  416,  A,  J ;  B,  4)  which  serves  to  store  up 
nutriment. 

Glands.  —  Besides  the  liver  and  pancreas,  there  are  a  number 
of  glands  in  the  body  of  the  frog  that  are  of  great  importance 
because  of  their  secretions.  These  glands  have  no  ducts,  but 
empty  their  products  directly  into  the  body;  they  are  therefore 
called  ductless  glands,  and  their  products  are  called  internal 
secretions.  Internal  secretions  are  also  produced  by  other 
organs,  e.g.  the  liver  forms  sugar  and  urea. 

The  spleen  is  a  reddish  body  situated  above  the  an1;erior  end 
of  the  cloaca.  In  it  old  blood  corpuscles  are  destroyed  and  new 
colorless  corpuscles  are  probably  formed. 

The  two  thyroid  glands  are  situated  one  on  either  side  of  the 
Hyoid.  Their  secretions  contain  a  large  amount  of  iodin.  The 
function  of  the  thyroid  is  not  certain  in  the  frog.  In  man  its 
atrophy  causes  a  disease  called  cretinism. 

The  two  thymus  glands  lie  one  behind  each  tympanum,  be- 
neath the  depressor  mandibulae  muscle.  Their  function  is  not 
certain. 

The  adrenal  bodies  are  long,  thin  glands  lying  on  the  ventral 
surface  of  the  kidneys.  They  secrete  adrenalin,  a  substance 
necessary  for  the  life  of  the  animal.  When  adrenalin  is  ex- 
tracted and  then  injected  into  the  blood  of  a  mammal,  it  causes 
a  contraction  of  the  blood-vessels  and  therefore  raises  the  blood 
pressure. 

The  Skeleton.  —  The  skeleton  of  the  frog  consists  principally 
of  bone.  The  axial  portion  comprises  the  skull  and  vertebral 
column.  The  appendicular  portion  consists  of  the  pectoral  and 
pelvic  girdles  and  the  bones  of  the  limbs  which  they  support. 


CLASS   AMPHIBIA 


493 


Fig.  418.  —  Skeleton  of  the  frog.  A,  skull  and  vertebral  column,  dorsal 
surface.  B,  skull  and  vertebral  column,  ventral  surface.  C,  side  view  of 
urostyle;  bristle  passes  through  opening  of  loth  spinal  nerve.  D,  visceral 
arches,  ar,  neural  arch;  av,  atlas;  c,  centrum;  ex,  exoccipital;  fm,  foramen 
magnum;  //,  basilingual  plate;  Ha,  hyoid  arch;  Hp,  thyrohyal;  mx,  maxilla; 
na,  nasal;  O,  orbital  fossa;  pal,  palatine;  par,  parasphenoid;  pf,  parieto- 
frontal; pmx,  premaxilla;  pro,  prootic;  ptg,  pterygoid;  qj,  quadratojugal; 
sp.  el,  sphenethmoid;  sq,  squamosal;  trv,  transverse  process;  ur,  urostyle; 
vo,  vomer;    zyg,  zygopophysis      (From  Bourne,  after  Ecker.) 


494  COLLEGE  ZOOLOGY 

The  cartilage  and  bones  of  the  skull  may  be  grouped  into  two 
main  divisions:  (i)  the  brain  case  and  auditory  and  olfactory 
capsules,  which  constitute  the  cranium;  and  (2)  the  jaws  and 
hyoid  arch,  which  constitute  the  visceral  skeleton. 

Cranium.  —  A  large  part  of  the  cranium  consists  of  cartilage 
(dotted  in  Fig.  418).  The  bones  are  either  ossifications  of  the 
cartilage  (the  exoccipitals  (ex),  prootics  (pro),  and  ethmoid), 
or  are  developed  from  membranes  and  invest  the  cartilage  and 
cartilage  bones.  The  spinal  cord  passes  through  a  large  open- 
ing, the  foramen  magnum  (Fig.  418,  fm),  in  the  posterior  end  of 
the  cranium.  On  either  side  of  this  opening  is  a  convexity  of 
the  exoccipital  bones  (ex),  called  the  occipital  condyle,  which 
articulates  in  life  in  a  concavity  of  the  first  vertebra  (av),  and 
enables  the  frog  to  move  its  head. 

The  cranial  bones  of  the  dorsal  side  are  the  prootics  (Fig.  418, 
pro)  which  inclose  the  inner  ears,  the  frontoparietals  (pf)  which 
form  most  of  the  roof  of  the  cranium,  the  sphenethmoid  (sp.  et) 
which  forms  the  posterior  wall  of  the  nasal  cavity,  and  the?  nasals 
(na)  which  lie  above  the  nasal  capsules.  The  ventral  surface  of 
the  cranium  discloses  the  central,  dagger-shaped  parasphenoid 
(par)  and  the  vomers  (vo)  which  bear  the  vomerine  teeth. 

The  Visceral  Skeleton.  —  The  jaws  and  hyoid,  which  con- 
stitute the  visceral  skeleton,  are  also  preformed  in  cartilage  and 
then  strengthened  by  ossifications.  The  upper  jaw  or  maxillary 
arch  consists  of  a  pair  of  premaxillce  (Fig.  418,  pmx),  a  pair  of 
maxillcB  (mx),  and  a  pair  of  quadratojugals  (qj).  The  maxillae 
and  premaxillae  bear  teeth.  The  lower  jaw  or  mandibular  arch 
consists  of  a  pair  of  cartilaginous  rods  (Meckel's  cartilages) 
invested  by  a  pair  of  dentary  bones,  and  a  pair  of  angulo-splenials. 
The  jaws  are  attached  to  the  cranium  by  a  suspensory  apparatus 
consisting  of  the  squamosals  (Fig.  418,  sq),  the  pterygoids  (ptg), 
and  the  palatines  (pal). 

The  visceral  arches  are  represented  in  the  adult  by  the  hyoid 
and  its  processes  (Fig.  418,  D).  The  cartilaginous  hasilingual 
plate  lies  in  the  floor  of  the  mouth  cavity.     The  hyoid  arches 


CLASS  AMPHIBIA  495 

(Fig.  418,  D,  Ea)  curve  upward  and  join  the  prootics  on  either 
side.  Two  ossified  posterior  processes,  the  thyrohyals  (Hp) 
help  support  the  larynx. 

The  Vertebral  Column  (Fig.  418).  —  The  vertebral  column 
consists  of  nine  vertebrce  and  a  blade-like  posterior  extension, 
the  urostyle.  The  vertebrae  consist  of  a  basal  centrum,  which 
is  concave  in  front  and  gonvex  behind  (procoelous  type),  and  a 
neural  arch  (Fig.  418,  ar)  through  which  the  spinal  cord  passes. 
The  neural  arch  possesses  a  short,  dorsal  spine,  sl  transverse 
process  (trv)  on  each  side  (except  on  the  first  vertebra,  av),  and 
a  pair  of  articulating  processes,  called  zygapophyses  {zyg),  at 
each  end.  The  vertebrae  are  held  together  by  ligaments,  and 
move  on  one  another  by  means  of  the  centra  and  zygapophyses. 
The  vertebral  column  thus  serves  as  a  firm  axial  support  which 
also  allows  bending  of  the  body. 

The  Appendicular  Skeleton.  —  The  pectoral  girdle  and 
sternum  (Fig.  419,  A)  support  the  fore  limbs,  serve  as  attach- 
ments for  the  muscles  that  move  the  fore  limbs,  and  protect  the 
organs  lying  within  the  anterior  portion  of  the  trunk.  They 
are  composed  partly  of  bone  and  partlv  of  cartilage.  The  supra- 
scapulae  lie  above  the  vertebral  column,  and  the  i*est  of  the  girdle 
passes  downwards  on  either  side  and  unites  with  the  sternum 
in  the  ventral,  middle  line.  The  principal  parts  are  the  supra- 
scapulcB  (Fig.  419,  A,  s.  sc),  the  scapulce  (sc),  the  clavicles  (cl), 
the  coracoids  {cor),  the  epicoracoids  (ep.c),  the  ommosternum  (os), 
episternum  (ep),  mesosternum  (mes),  and  xiphisternum  {xi). 
The  end  of  the  long  bone  of  the  fore  limb  {humerus)  lies  in 
a  concavity  in  the  scapula  and  coracoid  called  the  glenoid 
fossa  {gl). 

The  pelvic  girdle  (Fig.  419,  B)  supports  the  hind  limbs. 
It  consists  of  two  sets  of  three  parts  each,  the  ilium  {II),  the 
ischium  {Isch),  and  the  pubis  {Pu).  The  pubis  is  cartilaginous. 
The  anterior  end  of  each  ilium  is  attached  to  one  of  the  trans- 
verse processes  of  the  ninth  vertebra.  Where  the  parts  of  each 
half  of  the  pectoral  girdle  unite,  there  is  a  concavity,  called 


496 


COLLEGE  ZOOLOGY 


the  acetabulum  (Ac),  in  which  the  head  of  the  long  leg  bone 
(femur)  lies. 

The  fore  limbs  (Fig.  420,  A)  consist  of  a  humerus  which  articu- 
lates with  the  glenoid  fossa  of  the  pectoral  girdle  at  its  proximal 


Fig.  419.  —  Skeleton  of  the  frog.  A,  pectoral  girdle,  cl,  clavicle;  cor,  cora- 
coid;  ep,  episternum;  ep.c,  epicoracoid;  gl,  glenoid  cavity;  mes,  mesosternum; 
OS,  ommosternum;  sc,  scapula;  s.sc,  suprascapula;  xi,  xiphisternum.  B,  pelvic 
girdle,  side  view.  Ac,  acetabulum;  //,  ilium;  Isch,  ischium;  Pu,  pubis. 
(From  Bourne,  after  Ecker.) 


end  and  with  the  radio-ulna  (ru)  at  its  distal  end.  The  bone  of 
the  forearm  (radio-ulna)  consists  of  the  radius  and  ulna  fused. 
The  wrist  contains  six  bones:  the  ulnar e  (u),  radiate  (r),  inter- 


CLASS   AMPHIBIA 


497 


medium  (im),  and  three  car  pals  (a,  b,  c).  The  hand  is  supported 
by  five  proximal  metacarpal  bones,  followed  in  digits  II  and  III 
by  two  phalanges,  and  in  digits  IV  and  V  by  three  phalanges. 

The  hind  limbs  (Fig.  420,  B)  consist  of  (i)  a  femur  or  thigh 
bone,  (2)  a  tibio-fibula  (the  tibia  and  fibula  fused)  or  leg  bone, 
(3)  four  tarsal  bones,  — the  astragalus  {tibiale,  a),  the  calcaneum 


JZT 


JP      A 


Fig.  420.  —  Skeleton  of  the  limbs  of  the  frog.     A,  fore  limb,  a,  b,  c,  carpals ; 

im,    intermedium ;    r,    radiale ;    ru,     radis-ulna ;     J-V,    digits.  B,     hind    limb. 

a,  ostragalus ;  c,  calcaneum ;  I-V,  digits ;  X,  accessory  digit.  (From  Bourne, 
after  Ecker.) 

(fibulare,  b),  and  two  smaller  bones,  —  (4)  the  four  metatarsals  of 
the  foot,  (5)  the  phalanges  of  the  digits,  and  (6)  the  prehallux 
(X)  of  the  accessory  digit. 

The  Muscular  System  (Fig.  421).  —  Muscles  are  usually 
attached  by  one  or  both  ends  to  bones  either  directly  or  by  means 
of  a  tendon,  which  is  an  inelastic  band  of  connective  tissue.  The 
two  ends  of  a  muscle  are  designated  by  different  terms :  thg  origin 
is  the  end  attached  to  a  relatively  immovable  part;  the  insertion 
is  the  movable  end.    A  muscle  which  bends  one  part  upon 

2  JH 


Fig.  421.  —  Muscles  of'  the  frog,  ventral  view.  add.brcv,  adductor 
brevis;  add.long,  adductor  longus;  add. mag,  adductor  magnus;  del,  deltoid; 
ext.cr,  extensor  cruris;  ext.trs,  extensor  tarsi;  FE,  femur;  gn.hy,  geniohyoid; 
gstr,  gastrocnemius;  hy.gl,  hyoglossus;  ins. ten,  inscriptio  tendinea;  I. alb,  linea 
alba;  my.hy,  mylohyoid;  obl.int,  obliquus  internus;  obl.ext,  obliquus  ex- 
ternus;  o.sl,  ommosternum;  p.c.hy,  posterior  cornu  of  hyoid;  pet,  pectoralis; 
Petn,  pectineus;  per,  peronaeus;  rct.abd,  rectus  abdominis;  rect.int.maj,  rectus 
internus  major;  rect.int.min,  rectus  internus  minor;  sar,  sartorius;  sb.mt,  sub- 
mentalis;  sent  ten,  semi-tendinosus;  tib.ant,  tibialis  anticus;  iib.post,  tibialis 
posticus;  TI.FI,  tibiofibuhi;  vast.int,  vastus  internus;  x.st,  xiphisternum. 
(From   Parker   and   Haswell.) 

498 


CLASS  AMPHIBIA 


499 


another,  as  the  leg  upon  the  thigh,  is  a  Hexor:  one  that  straightens 
out  a  part,  as  the  extending  of  the  foot,  is  an  extensor ;  one  that 
draws  a  part  back  toward  the  median  line  is  an  adductor:  one 
that  pulls  a  part  forward  toward  the  median  line  is  an  abductor; 
one  that  lowers  a  part  is  a  depressor :  one  that  raises  a  part  is  a 
levator :  and  one  that  rotates  onopart  on  another  is  sl  rotator. 
The  movements  of  an  organ  depend  on  the  origin  and  insertion 
of  the  muscles  and  the  nature  of  the  articulations  of  its  bones 
with  each  other  and  with  other  parts  of  the  body. 

The  muscles  of  the  hind  limb  are  usually  selected  for  study 
to  illustrate  the  methods  of  action  of  muscles  in  general.  Table 
XVI  gives  the  name,  origin,  insertion,  and  action  of  the  principal 
muscles  of  the  hind  limb,  and  Figure  421  shows  most  of  them  as 
seen  from  the  ventral  side. 


TABLE  XVI 

THE  NAME,   ORIGIN,  INSERTION,  AND  ACTION  OF  THE  PRINCIPAL 
MUSCLES   OF   THE   HIND   LIMB    OF   THE    FROG 


Name 

Origin 

Insertion 

Action 

Sartorius(Fig.  421, 
sar) 

Ilium,     just 
in  front  of 
pubis 

Just  below  head 
of  tibia 

Flexes  leg ;  draws 
leg  forward  and 
ventrally 

Adductor  magnus 
(add.mag) 

Pubis,        is- 
chium, and 
tendon     of 
semimem- 
branosus 

Distal  end  of 
femur 

Bends  thigh  ven- 
trally, adducts  or 
abducts  femur 
according  to 
position  of  latter 

Adductor     longus 
{addlong) 

Ventral  part 
of  ilium 

Joins  adductor 
magnus. 

Abducts  thigh ; 
draws  thigh  ven- 
trally. 

Triceps  femoris 

From     three 
heads,    one 
acetabulum, 
two  ilium 

Upper  end  of 
tibio-fibula ; 
tendon  of  gas- 
trocnemius 

Extends  and  ab- 
ducts leg 

500 


COLLEGE  ZOOLOGY 


Name 

Origin 

Insertion 

Action 

Gracilis  major 
(rect.int.maj.) 

Posterior 
margin    of 
ischium 

Proximal    end 
of  tibia ;  head 
of  tibio-fibula 

Adducts  thigh ; 
flexes  or  extends 
leg  according  to 
position  of  latter 

Gracihs  minor 
{rect.int.min.) 

Tendon    be- 
hind       is- 
chium 

Joins  tendon  of 
gracilis  major 

Same  as  gracilis 
major 

Semimembranosus 

Dorsal  half 
of  ischium 

Proximal    end 
tibio-fibula 

Same  as  gracilis 
major 

Ileo-fibularis 

Behind   dor- 
sal crest  of 
ilium 

Proximal    end 
of  fibula 

Draws  thigh  dor- 
sally  ;  flexes  leg 

Semitendinosus 
{sem.ten) 

Two    points 
on  ischium 

Proximal    end 
of  tibia 

Adducts  thigh ; 
flexes  leg 

Pyriformis 

Tip  of    uro- 
style 

Near  proximal 
end  of  femur 

Pulls  urostyle  to 
one  side;  draws 
femur  dorsally 

Iliacus  externus 

Outer  side  of 
dorsal  crest 
of  ilium 

Head  of  femur, 
posterior  side 

Rotates  femur  for- 
ward 

Iliacus  internus 

Ventral  bor- 
der of  ilium 

Proximal   half 
of  femur 

Draws  thigh  for- 
■    ward 

Gastrocnemius 
{gstr) 

Distal      end 
femur;  ten- 
don of  tri- 
ceps 

By  broad  ten- 
don on  sole  of 
foot 

Flexes  leg ;  ex- 
tends foot 

Tibialis   posticus 
(iib.post) 

Posterior  side 
of       tibio- 
fibula 

Proximal    end 
of  astragalus 

Extends  foot  when 
flexed ;  flexes 
foot  when  fully 
extended 

Tibialis  anticus 
longus  {tib.ant) 

Distal  end  of 
femur 

Proximal    end 
of  astragalus 
and      calca- 
neum 

Extends  leg ;  flexes 
foot 

CLASS  AMPHIBIA 


501 


Name 

Origin 

Insertion 

Action 

Peroneus  {per) 

Distal  end  of 
femur 

Distal  end  fe- 
mur ;  head  of 
calcaneum 

Extends   leg   and 
foot ;   flexes  foot 

Extensor  cruris 
{ext.cr) 

Distal  end  of 
femur 

Anterior  sur- 
face of  tibio- 
fibula 

Extends  foot 

Tibialis  anticus 
brevis 

Distal    third 
of       tibio- 
fibula 

Proximal  end 
of  astragalus 

Flexes  foot 

The  following  are  a  few  of  the  muscles  of  the  other  parts  of 
the  body:  The  rectus  abdominis  (Fig.  421,  rct.abd)  extends 
along  the  ventral  side  of  the  trunk;  the  obliquus  externus  {obi. 
ext)  covers  most  of  the  sides  of  the  trunk;  the  transversus  {obi. 
int)  lies  beneath  the  obliquus  externus  and  serves  to  contract 
the  body-cavity;  the  pedoralis  major  {pet)  moves  the  fore  limbs; 
and  the  submaxillary  {my.hy)  raises  the  floor  of  the  mouth 
cavity  during  respiration.    , 

The  Nervous  System.  — v  Three  main  divisions  may  be  dis- 
tinguished in  the  nervous  system  of  the  frog:  (i)  the  central , 
consisting  of  the  brain  and  spinal  cord;  (2)  the  peripheral,  con-  , 
sisting  of  the  cerebral  and  spinal  nerves;  and  (3)  the  sympathetic.) 
It  will  be  sufficient  in  this  place  to  point  out  certain  selected 
points  concerning  the  nervous  system  of  the  frog,  since  general 
accounts  of  nervous  tissue  (p.  76),  nervous  activity  (pp.  223-226), 
and  the  nervous  system  of  vertebrates  (pp.  408^410)  have 
already  been  given. 

The  Brain. — The  brain  (Fig.  422)  has  two  large  olfactory 
lobes  which  are  fused  together,  two  large  cerebral  hemispheres, 
two  large  optic  lobes,  a  well-developed  midbrain  {ZH),  a 
very  small  cerebellum,  and  a  medulla  oblongata,  which  is  pro- 
duced by  the  broadening  of  the  spinal  cord.  The  optic 
chias?na  (Fig.  422,  B,  Tr.opt),  the  infundibulum  {Jnf),  and  the 


502 


COLLEGE  ZOOLOGY 


hypophysis  ( Hyp)  are  visible  only  on  the  ventral  surface  of  the 
brain. 

The  functions  of  the  different  parts  of  the  frog's  brain  have 
been  partially  determined  by  experiments  in  which  the  parts 
were  removed  and  the  effects  upon  the  animals  observed.     It  is 


' — ol.  lobe 


cerebrum 


zn— 

IB     Tr.ojjf : 

optic  lobe 


erebellum 


ol.  lobe 


'Cerebrum 


— # 


—optic  lobe 


Jlrjji 


medulla      371- 


~Mi 


Fig.  422.  —  Brain  of  the  frog.  A,  dorsal  aspect.  B,  ventral  aspect. 
I-XII,  nerves;  Hyp,  hypophysis;  Jnf,  infundibulum;  Med,  NH,  medulla 
oblongata;  Tr.opt,  optic  tract;  ZH,  diencephalon.  (From  Davenport,  after 
Wiedersheim.) 


not  certain  what  the  functions  of  the  cerebral  hemispheres  are 
in  the  frog.  They  are  the  seat  of  intelligence  and  voluntary 
control  in  higher  animals.  When  the  midbrain  is  reinoved 
along  with  the  cerebral  hemispheres^  the  frog  loses  the  power 
of  spontaneous  movement.  When  the  optic  lobes  are  removed, 
the  spinal  cord  becomes  more  irritable;   this  shows  that  these 


CLASS  AMPHIBIA 


503 


lobes  have  an  inhibiting  influence  on  the  reflex  activity  of  the 
spinal  cord.  The  cerebellum  apparently  has  no  important  func- 
tion in  the  frog.  Many  activ- 
ities are  still  possible  when 
everything  but  the  medulla 
is  removed.  The  animal 
breathes  normally,  snaps  at 
and  swallows  food,  leaps  and 
swims  regularly,  and  is  able 
to  right  itself  when  thrown 
on  its  back.  Extirpation  of 
the  posterior  region  of  the 
medulla  results  in  the  early 
death  of  the  frog.  The  brain 
as  a  whole  controls  the  actions 
effected  by  the  nerve-centers 
of  the  spinal  cord.  "  The 
higher  centers  of  the  brain 
are  comparable  to  the  cap- 
tain of  a  steamer  who  issues 
orders  to  the  man  running 
the  engine  when  to  start  and 
when  to  stop,  and  who  has 
his  hand  on  the  wheel  so  as 
to  guide  the  course  of  the 
vessel."  (Holmes.)  Cranial 
nerves  I  to  X  (see  p.  409, 
Table  XIV)  are  present  in 
the  frog. 
The    Spinal    Cord    (Fig. 

423). — The   spinal    cord   ex-    frog.       Br,  brachial    nerve;    Js,  ischial 

tends    backward    from    the   ^^^^^  'i:Lf'-C:"Z  "Zal 

medulla  and  ends  in  the  uro-     nerve;    Sgi-io,'  ten    ganglia    of  sympa- 

Stvle       Tt    is    surrounded    hv    ^^^^'^   system;    Vg,  gasserian    ganglion; 
Styie.      11    IS    SUrrounaea    Oy    ^^^  ganglion    of    vagus.       (From    Sedg- 

two     membranes,     an     outer     wick's  Zoology,  after  Ecker.) 


7/ '"'    \ 

Fig.  423.  —  Nervous    system    of    the 


504  COLLEGE  ZOOLOGY 

dura  mater  and  an  inner  pia  mater.  The  cord  is  composed  of 
a  central  mass  of  gray  matter  (Fig.  349,  gm)  consisting  mainly 
of  nerve-cells,  and  an  outer  mass  of  white  matter  made  up  chiefly 
of  nerve-fibers.  A  median  fissure  occurs  both  in  the  dorsal  and 
in  the  ventral  side  of  the  cord,  and  a  central  canal  (c.c)  Ues  in 
the  gray  matter  and  communicates  anteriorly  with  the  cavities 
of  the  brain. 

The  Spinal  Nerves.  —  The  relation  of  the  spinal  nerves  to 
the  spinal  cord  and  the  paths  taken  by  nervous  impulses  are 
indicated  in  Figure  349.  There  are^ten  pairs  of  spinal  nerves 
in  the  frog  (Fig.  423,  Spni,  Br,  Js).  Eacli  arises  by  a  dorsal 
(Fig.  349,  d.r)  and  a  ventral  (v.r)  root  (see  p.  408)  which  spring 
from  the  horns  of  the  gray  matter  of  the  cord.  The  two  roots 
unite  to  form  a  trunk,  which  passes  out  between  the  arches 
of  adjacent  vertebrae.  The  largest  nerves  are  the  brachial 
(Fig.  423,  Br),  which  are  composed  of  the  second  and  branches 
from  the  first  and  third,  pairs  of  spinal  nerves,  and  are  dis- 
tributed to  the  fore  limbs  and  shoulder,  and  the  sciatics  (Js), 
which  arise  from  plexuses  composed  of  the  seventh,  eighth, 
and  ninth  spinal  nerves,  and  are  distributed  to  the  hind 
limbs. 

The  Sympathetic  System  (Fig.  423,  Sgi-io). — This 
system  consists  of  two  principal  trunks,  which  begin  in  the 
prootic  ganglion  and  extend  posteriorly,  one  on  either  side  of  the 
vertebral  column.  Eacji^unk  is  provided  with  ten  gan^ionic 
enlargements  (Sgi-io)  at  the  points  where  branches  from  the 
spinal  nerves  unite  with  it.  The  nerves  of  the  sympathetic 
system  are  distributed  to  the  internal  organs  which  are  thus 
intimately  connected. 

Sense-organs.  —  The  principal  sense-organs  are  the  eyes, 
ears,  and  olfactory  organs.  There  are  many  smaller  structures 
on  the  surface  of  the  tongue,  and  on  the  floor  and  roof  of  the 
mouth,  which  probably  function  as  organs  of  taste.  In  the  skin 
are  also  many  sensory  nerve  endings  which  receive  contact, 
chemical,   temperature,  and  light  stimuli. 


CLASS  AMPHIBIA  505 

The  Olfactory  Organs.  —  The  olfactory  nerves  (Fig.  423, 
01)  extend  from  the  olfactory  lobe  of  the  brain  (Fig.  422)  to  the 
nasal  cavities  (Fig.  412,  olf.s),  where  they  are  distributed  to 
the  epithelial  lining.  The  importance  of  the  sense  of  smell  in 
the  life  of  the  frog  is  not  known. 

The  Ear.  —  The  inner  ear  of  the'  frog  lies  within  the  auditory 
capsule  and  is  protected  by  the  prootic  (Fig.  418,  pro)  and  ex- 
occipital  {ex)  bones.  It  is  similar  in  structure  to  that  shown 
in  Figure  350,  page  411,  and  is  supplied  by  branches  of  the 
auditory  nerve.  There  is  no  external  ear  in  the  frog.  The 
middle  ear  is  a  cavity  which  communicates  with  the  mouth 
cavity  through  the  Eustachian  tube  (Fig.  411,  E),  and  is  closed 
externally  by  the  tympanic  membrane. 

A  rod,  the  columella,  extends  across  the  cavity  of  the  middle 
ear  from  the  tympanic  membrane  to  the  inner  ear.  The  vi- 
brations of  the  tympanic  membrane  produced  by  sound  waves 
are  transmitted  to  the  inner  ear  through  the  columella.  The 
sensory  end  organs  of  the  auditory  nerve  are  stimulated  by  the 
vibrations,  and  the  impulses  carried  to  the  brain  give  rise  to  the 
sensation  of  sound.  The  inner  ears  serve  also  as  organs  of 
equilibration.  Frogs  from  which  they  are  removed  cannot  main- 
tain an  upright  position. 

The  Eye.  —  The  eyes  of  the  frog  resemble  those  of  man  in 
general  structure  and  function  (Fig.  351,  pp.  411-413),  but  differ 
in  certain  details.  The  eyeballs  lie  in  cavities  (orbits.  Fig.  418,  O) 
in  the  sides  of  the  head.  They  may  be  rotated  by  six  muscles 
and  also  pulled  into  the  orbit.  The  upper  eyelid  does  not  move 
independently.  The  lower  eyelid  consists  of  the  lower  eyelid 
proper  fused  with  the  third  eyelid  or  nictitating  membrane.  The 
lens  is  large  and  almost  spherical.  It  cannot  be  changed  in 
form  nor  in  position,  and  is  therefore  fitted  for  viewing  distinctly 
objects  at  a  certain  definite  distance.  Movements  are  noted 
much  oftener  than  form.  The  amount  of  light  that  enters  the 
eye  can  be  regulated  by  the  contraction  of  the  pupil.  The 
retina  of  the  eye  is  stimulated  by  the  rays  of  hght  which  pass 


5o6  COLLEGE  ZOOLOGY 

through  the  pupil,  and  the  impulses  which  are  carried  through 
the  optic  nerve  to  the  brain  give  rise  to  sensations  of  sight. 

Behavior.  —  The  activities  of  the  frog  are  such  as  to  enable 
it  to  exist  within  the  confines  of  its  habitat.  The  ordinary- 
movements  are  those  employed  in  leaping,  diving,  crawling, 
burrowing,  and  maintaining  an  upright  position.  These  and 
most  of  its  other  activities  may  be  resolved  into  a  series  of  reflex 
acts,  although  they  are  commonly  said  to  be  instinctive.  In- 
stinct is  "  the  faculty  of  acting  in  such  a  way  as  to  produce  cer- 
tain ends,  without  foresight  of  the  ends,  and  without  previous 
education  in  the  performance."     (James.) 

Some  of  the  movements  of  the  frog  are  due  to  internal  causes, 
but  many  of  them  are  the  responses  to  external  stimuli.  Frogs 
are  sensitive  to  light,  and  experiments  have  shown  that  both  the 
eyes  and  skin  are  stimulated  by  it.  The  reaction  to  light  causes 
the  animal  to  orient  its  body  so  that  it  faces  the  source  and  is  in 
line  with  the  direction  of  the  rays.  Nevertheless,  frogs  tend  to 
congregate  in  shady  places.  Frogs  also  seem  to  be  stimulated 
by  contact  (thigmotropism,  p.  36),  as  shown  by  their  tendency 
to  crawl  under  stones  and  into  crevices.  The  desire  for  shade 
may,  however,  have  some  influence  upon  this  reaction.  The 
temperature  modifies  the  responses  both  to  light  and  to  contact. 

Investigators  who  have  studied  the  behavior  of  frogs  have 
come  to  the  conclusion  that  they  are  very  stupid  animals.  It 
is  possible  to  teach  them  certain  things,  and  habits  once  formed 
are  not  easily  changed.  For  example,  Yerkes  found  that  a  frog 
could  learn  to  follow  a  path  in  a  labyrinth  after  about  one  hun- 
dred trials.  If  we  consider  the  power  to  learn  by  individual 
experience  as  evidence  of  the  presence  of  mind,  then  we  must 
attribute  a  primitive  sort  of  mind  to  the  frog. 

Development.  —  Frogs  lay  their  eggs  in  water  in  the  early 
spring.  The  male  clasps  the  female  firmly  with  his  fore  legs 
just  behind  her  fore  legs.  After  the  male  has  been  carried  about 
by  the  female  for  several  days,  the  eggs  pass  from  the  uterus  out 
of  the  cloaca  and  are  fertilized  by  the  spermatozoa  of  the  male, 


CLASS  AMPHIBIA 


507 


which  the  latter  discharges  over  them  as  they  are  extruded. 
The  male  then  loses  the  clasping  instinct  and  leaves  the  female. 
The  jelly  which  surrounds  and  protects  the  eggs  soon  swells 
up  through  the  absorption  of  water.  Cleavage  takes  place  as 
indicated  in  Figure  424.  Some  of  the  cells,  called  macromeres 
(Fig.  425,  A,  mg),  are  large  because  of  a  bountiful  supply  of  yolk; 
others,  the  micromeres  {mi),  are  smaller.  A  blastula  (Fig.  425, 
A)  is  formed  by  the  appearance  of  a  cavity,  the  blastocoel  {hi. 
cosl),  near  the  center  of  the  egg.  Gastrulation  is  modified  in  the 
frog's  egg  because  of  the  amount  of  yolk  present.     The  dark 


Fig.  424. 


Segmentation  of  the  frog's  egg.     (From  Sedgwick's  Zoology, 
after  Ecker.) 


side  of  the  egg  gradually  grows  over  the  lighter  portion  until 
only  a  circular  area  of  the  latter,  called  the  yolk  plug  (Fig.  425, 
yk.pl),  is  visible.  This  gastrula  contains  two  germ-layers,  an 
outer  ectoderm  (C,  ect)  and  an  inner  entoderm  (C,  end).  A  third 
layer,  the  mesoderm  (C,  mes),  soon  appears  between  the  other  two, 
and  splits  into  two,  an  inner  splanchnic  layer,  which  forms  the 
supporting  tissue  and  musculature  of  the  alimentary  canal,  and 
an  outer  somatic  or  parietal  layer,  which  forms  the  connective 
tissue,  muscle,  and  peritoneum  of  the  body-wall.  The  cavity 
between  these  two  mesodermal  layers  is  the  ccelom. 

Soon  after  gastrulation  a  groove  called  the  primitive  or 
medullary  groove  (Fig.  425,  B,  md.gr)  appears,  on  either  side  of 
which  is  a  medullary  fold  {md.f).  The  medullary  folds  grow 
together  at  the  top,  forming  a  tube  which  later  develops  into  the 
brain  and  spinal  cord  of  the  embryo.     The  medullary  groove  lies 


5o8 


COLLEGE  ZOOLOGY 


along  the  median  dorsal  line,  and  the  embryo  now  lengthens  in 
this  direction.  The  region  where  the  yolk  plug  was  situated 
lies  at  the  posterior  end.  On  either  side  near  the  anterior  end 
two  gill-arches  appear  (Fig.  425,  D,  hr.cl),  and  in  front  of  each 
of  these  a  depression  arises  which  unites  with  its  fellow  and 

ect 
nch, 


bl.coel 


stilni 


Fig.  425.  —  Development  of  the  embryo  of  the  frog.  A,  section  of  blastula. 
hl.cod,  blastocoel;  mi,  micromeres;  mg,  macromeres.  B,  formation  of  medul- 
lary groove,  md.gr,  and  medullary  fold,  md.f;  yk.pl,  yolk-plug.  C,  section 
of  egg  in  stage  B  to  show  germ-layers,  bl.ccel,  blastocoel ;  blp,  blastopore; 
ect,  ectoderm;  end,  entoderm;  eni,  enteron;  mes,  mesoderm;  nch,  notochord; 
yk.pl,  yolk-plug.  D,  older  embryo,  br.cl,  branchial  arches;  stdm,  stomo- 
daeum;  /,  tail.  E,  newly  hatched  tadpole.  br,i,  br.2,  gills;  e,  eye;  pcdm,  procto- 
daeum;  sk,  sucker;  stdm,  stomodaeum;  /,  tail.  (From  Parker  and  Haswell; 
A,  D,  after  Ziegler's  models;   B,  C,  E,  after  Marshall.) 


moves  to  the  ventral  surface,  becoming  the  ventral  sucker  (Fig. 
425,  E,  sk).  An  invagination  soon  appears  just  above  the 
ventral  sucker;  this  is  the  stomodceum  {stdm)  which  develops 
into  the  mouth. 

The  invagination  (proctodcBum,  Fig.  425,  E,  pcdm)  which 
becomes  the  anus  appears  beneath  the  tail  (/)  at  the  posterior 
end.     On  either  side  above  the  mouth  a  thickening  of  the 


CLASS  AMPHIBIA 


509 


ectoderm  represents  the  beginning  of  the  eye,  and  just  above  the 
gills  (E,  hr.i,  hr.2)  appear  the  invaginations  which  form  the 
vesicles  of  the  inner  ears.  The  markings  of  the  muscle  segments 
show  through  the  skin  along  the  sides  of  the  body  and  tail. 


Fig.  426.  —  Tadpoles  in  different  stages  of  development,  from  those  just 
hatched  (i)  till  the  adult  form  is  attained  (8).     (From  Mivart.) 


The  embryo  moves  about  within  the  egg  by  means  of  cilia, 
but  these  soon  disappear  after  hatching.  The  tadpole,  after 
breaking  out  of  the  egg  membranes,  lives  for  a  few  days  on  the 
yolk  in  tWb  alimentary  canal,  and  then  feeds  on  algae  and  other 
vegetable  matter.  The  external  gills  grow  out  into  long,  branch- 
ing tufts  (Fig.  426,  2,  2  a).    Four  pairs  of  internal  gills  are  formed 


5IO  COLLEGE  ZOOLOGY 

later,  and,  when  the  external  gills  disappear,  these  function  in 
their  stead,  the  water  entering  the  mouth,  passing  through  the 
gill-slits,  and  out  of  an  opening  on  the  left  side  of  the  body,  called 
the  spiracle. 

The  hind  limbs  appear  first  (Fig.  426,  5).  Later  the  fore 
limbs  break  out  (6).  The  tail  decreases  in  size  as  the  end  of  the 
larval  period  approaches  and  is  gradually  resorbed  (7).  The 
gills  are  likewise  resorbed,  and  the  lungs  develop  to  take  their 
place  as  respiratory  organs.  Finally  the  form  resembling  that 
of  the  adult  frog  (8)  is  acquired. 

2.  A  Brief  Classification  of  Living  Amphibia  ^ 

There  are  about  one  thousand  different  species  of  Amphibia  — 
a  number  very  much  smaller  than  that  of  the  other  principal 
classes  of  vertebrates.  Approximately  forty  of  these  belong  to 
the  order  Apoda,  one  hundred  to  the  Caudata,  and  nine  hun- 
dred to  the  Salientia. 

Order  i.  Apoda  (Gymnophiona,  Fig.  427). — Ccecilians. — 
Worm-like  Amphibia  without  limbs  or  limb-girdles; 
usually  with  small  scales  embedded  in  the  skin;  tail 
short  or  absent. 
Family  CcECiLiiDiE.  —  With  the  characters  of  the  order. 
Examples:  Dermophis,  Ccecilia,  Gymnopis,  Siphonops, 
Ichthyophis  (Fig.  427). 

Order  2.  Caudata  (Urodela,  Figs.  428-433).  — Tailed  Am- 
phibia. Amphibia  with  a  tail ;  without  scales;  usually 
two  pairs  of  limbs;  the  adults  with  or  without  external 
gills  and  gill  slits. 
Suborder  i.  Proteida  (Fam.  Proteid^,  Fig.  428).  — Mud- 
puppies. — Tailed  Amphibia  with  two  pairs  of  limbs; 
three  pairs  of  external  gills  and  two  pairs  of  gill-open- 
ings persistent;  no  eyelids. 

1 1  am  indebted  to  Dr.  Alexander  G.  Ruthven  for  the  main  divisions  of  this 
classification. 


CLASS   AMPHIBIA  511 

Family  Proteid^.  —  With  characters  of  the  suborder. 
Examples:  Necturus,  Proteus,  Typhlomolge. 
Suborder  2.  Meantes  (Fam.  Sirenidae,  Fig.  429).  —  Sirens. 
— Tailed  Amphibia  without  hind  limbs;  three  pairs  of 
external  gills  and  three  pairs  of  gill-openings  persistent; 
no  eyelids.  '^ 

Family  Sirenid^,  —  With  the  characters  of  the  suborder. 
Examples:    Siren ,   Pseudobranchus. 
Suborder  3.   Mutabilia  (Fam.   Salamandrid^,   Figs.  43a- 
433).  —  Salamanders. — Tailed   Amphibia  with   tw^o 
pairs  of  limbs;    without  gills  and   generally  without 
gill-openings   in   adult  ;    usually   with   movable   eye- 
lids. 
Superfamily  i.   AMPmuMOiDEiE.  —  Mutabilia  with  two 
pairs  of  small  limbs;   sometimes  one  pair  of  gill-open- 
ings;   vertebrae   amphiccelous ;   without  eyelids. 

Family  Cryptobranchid^.  —  With  the  characters  of  the 
superfamily.  Examples:  Cryptohranchus  (Fig.  430), 
Amphiuma. 
Superfamily  2.  SALAMANDROiDEiE.  —  Mutabilia  with- 
out gills  or  gill-openings  in  the  adult;  with  movable 
eyelids;  vertebrae  usually  opisthocoelous.  The  families 
are  distinguished  from  one  another  principally  by  the 
position  of  the  teeth  and  the  number  of  toes. 

Family     i.     Salamandrid^e.  —  Examples:      Salamandra, 
Triton  (Fig.  431),  Diemyctylus. 

Family  2.   Ambystomid^. — Examples:   Amby stoma  (Fig. 
432),  Chondrotus. 

Family  3.  Plethodontid^.  —  Examples :  Plethodon,  S pe- 
ter pes,  Desmognathus  (Fig.  433). 
Order  3.  Salientia  (Anura,  Figs.  434-436). — Tailless  Am- 
phibia. Amphibia  without  a  tail ;  without  scales ;  two 
pairs  of  limbs;  without  external  gills  or  gill-openings  in 
adult. 
Suborder    i.   Aglossa.  —  Salientia     without     a     tongue; 


512  COLLEGE  ZOOLOGY 

Eustachian  tubes  open  by  single  aperture;  no  distinct 

tympanic   membrane;    vertebrae   opisthocoelous. 
Family  Aglossid^.  —  With  the  characters  of    the  sub- 
order.    Examples:    Pipa  (Fig.  434),  Xenopus. 
Suborder    2.   Linguata     (Phaneroglossa).  —  Frogs     and 

Toads.     Salientia  with  a  tongue;    Eustachian  tubes 

open  by  two  apertures. 
Family  I.   Pelobatid^e.  —  Spade-foot    toads.    Examples: 

Pelobates,  Scaphiopus. 
Family  2,  Bufonid^. — Toads.     Examples:    Bufo,  Rhi- 
y^^  nophrynus. 
Family  3.   Hylid^.  —  Tree-frogs.      Examples:     Acris, 

Chorophilus,   Hyla,  Nototrema  (Fig.  435). 
Family    4.   Cystignathid^.      Examples:     Hemiphradus, 

Hy lodes,    Paludicola. 
Family    5.   Engystomatid^.       Examples:        Engy stomas 

Phryniscus,  Hypopachus. 
Family  6.   Ranid^.  —  True    Frogs.     Examples:    Rana, 

Phyllobates,  Oxyglossus. 
Suborder  3.   Costata    (Discoglossid^e).  —  Salientia  with 

a  tongue;    Eustachian  tubes  open  by  two  apertures; 

with  short  ribs. 
Family   Discoglossid^e.  —  With    the   characters    of   the 

suborder.     Examples:     Discoglossus,     Alytes,     Bom- 

binator. 


3.  Review  of  the  Orders  and  Families  of  Living 
Amphibia 

Order  i.  Apoda. — The  single  family,  Cceciliid^e,  of  this 
order  includes  about  forty  species  of  worm-like  or  snake-like  leg- 
less Amphibia.  They  inhabit  the  tropical  regions  of  America, 
Africa,  India,  Burma,  and  northern  Australasia,  but  none  occurs 
in  the  United  States.  They  burrow  in  moist  ground  with  their 
strong  heads,  and,  as  a  result  of  living  in  darkness,  their  eyes  are 


CLASS   x\MPHIBIA 


513 


small  and  concealed  under  the  skin  or  maxillary  bones.     A 

sensory  tentacle  which  can  be  protruded  from  between  the  eyes 

and  the  nose  aids  the  animal  in  crawling  about.     They  feed  on 

small  invertebrates.     Most  of   the 

coecilians   lay  eggs,   but   some  ^re 

viviparous.      Ichthyophis    glutinosa 

(Fig.   427),   which   lives   in   India, 

Ceylon,  and  the  Malay  Islands,  and 

is  about  one  foot  long,  has  been 

more   carefully   studied    than   any 

other  species. 

Order  2.  Caudata.  —  The  tailed 
Amphibia  differ  so  widely  from  one 
another  that  it  has  been  found 
necessary  to  recognize  three  sub- 
orders. 

Suborder  i.  Proteida. — This  suborder  contains  a  single 
family,  Proteid^e,  the  mud-puppies,  and  three  genera,  Nedurus, 
Typhlomolge,  and  Proteus,  with  one  species  each.  Nedurus 
maculosus  (Fig.  428)  is  confined  to  the  rivers  and  lakes  of  the 
northern  and  eastern  part  of  the  United  States,  west  of  the  AUe- 
ghanies.  It  breathes  by  means  of  bushy  red  gills  which  extend 
out  from  in  front  of  the  fore  legs.  The  food  of  Nedurus  consists 
chiefly  of  crustaceans,  frogs,  worms,  insects,  and  small  fishes. 
During  the  day  the  mud-puppy  lies  concealed  in  a  dark  place. 


Fig.  427.  —  A  legless  am- 
phibian, Ichthyophis  glutinosa, 
female  guarding  her  eggs.  (From 
the  Cambridge  Natural  History, 
after  Sarasin.) 


Fig.  428.  —  The  "  mud-puppy,"  Nedurus  maculosus.     (From  Mivart.) 


but  at  night  it  swims  or  crawls  about  with  wavy  movements 
of  the  body. 

Proteus  anguinus  is  a  protean  about  one  foot  long,  which  has 
2  L 


514 


COLLEGE   ZOOLOGY 


been  found  only  in  the  caves  of  Austria.  It  is  white,  but  if 
exposed  to  the  Ught  may  become  dark  and  ultimately  black. 
It  has  rudimentary  eyes. 

Typhlomolge  rathbuni  is  a  blind  protean  that  came  up  with  the 
water  of  an  artesian  well  one  hundred  and  eighty-eight  feet  deep, 
in  Texas.  It  probably  feeds  on  the  crustaceans  in  under- 
ground streams,  since  four  species  of  these,  all  new  to  science, 
came  up  along  with  the  amphibians. 

Suborder  2.  Meantes.  —  This  suborder  also  contains  a  single 
family,  Sirenid^,  the  sirens,  and  two  genera.  Siren  and  Pseudo- 

branchus,  with  one 
species  each.  Siren 
lacertina  (Fig.  429), 
the  "  mud-eel,"  bur- 
rows in  the  mud  of 
ditches  and  ponds, 
and  swims  by  un- 
dulations of  the 
body.  It  has  three 
pairs  of  gill-shts  and  four  toes,  and  reaches  a  length  of  two 
and  one  half  feet.  It  inhabits  the  ponds  and  rivers  from 
Texas  to  North  Carolina.  Psendobranchus  striatus  has  but 
one  pair  of  gill-slits  and  only  three  toes.  It  has  been  found 
in  Georgia  and  Florida. 

Suborder  3.  Mutabilia.  —  Family  Cryptobranchid^.  — 
There  are  three  genera,  Cryptobranchus,  Megalobatrachus,  and 
Amphiuma.  Cryptobranchus  alleghaniensis,  the  hellbender  (Fig. 
430),  occurs  only  in  the  streams  of  the  eastern  United  States. 
It  reaches  a  length  of  from  eighteen  to  twenty  inches.  Its  food 
consists  of  worms  and  small  fish.  Megalobatrachus  maximus  is 
the  giant  salamander  of  Japan,  the  largest  of  all  the  Amphibia. 
It  feeds  on  fishes,  amphibians,  worms,  and  insects,  and  may 
reach  a  length  of  over  five  feet.  Amphiuma  means,  the  Congo 
"  snake,"  is  long  and  eel-shaped,  and  possesses  two  widely 
separated  pairs  of  small  legs.     It  occurs  in  the  marshes  and 


Fig.  429.  —  The  *'  mud-eel,"  Siren  lacertina. 
(From  the  Cambridge  Natural  History.) 


CLASS  AMPHIBIA 


515 


muddy  streams  of   the  southeastern  United   States,  and  feeds 
on  crayfishes,  moUusks,  and  small  fish. 


Fig.  430. — The  "  hellbender,"  Cryptobranchus.     (From  Davenport,  after 
the  Standard  Natural  History.) 


Family  Salamandrid^.  —  This  family  contains  the  true 
salamanders  and  the  newts  or  tritons.  "  Of  the  twenty- five 
species,  only  two  are  American,  four  are  eastern  Asiatic,  and 
of  the  remaining  nineteen,  two  are  Algerian,  while  the  rest  live 
in  Europe  or  in  Asia  Minor."  (Gadow.)  The  two  American 
species  are  Diemyctylus  viridescens  and  Triton  torosus. 

Diemyctylus  viridescens,  the  crimson-spotted  newt,  is  common 
in  the  ponds  of  the  northern  and  eastern  portions  of  the  United 
States.  It  is  about  three  and  one  half  inches  long  and  has  a  row 
of  crimson  spots  on  either  side.  Its  food  consists  principally 
of  insect  larvae,  worms,  and  small  mollusks.  The  eggs  are 
laid  in  April,  May,  or  June,  and  a  sort  of  "  nest  "  of  aquatic 
vegetation  is  constructed  for  each  egg.  The  young  live  for  a 
time  on  land  under  stones  and  logs,  but  return  to  the  water  after 
several  years,  becoming  aquatic  adults. 


5i6 


COLLEGE  ZOOLOGY 


Triton  torosus,  the  newt  of  western  North  America,  is  a  large 
species  reaching  a  length  of  six  inches.     It  feeds  on  earthworms. 

The  common 
fire  salamander  of 
Europe  is  Sala- 
mandra  maculosa, 
a  species  about  six 
inches  long.  It  is 
black,  with  bright 
yellow  spots,  and 
the  glands  of  the 
skin  secrete  a 
poisonous     sub- 


FiG.  431.  —  Triton  cristata.  i,  female;  2,  male  as  he 
appears  during  the  breeding  season.  (From  Shipley 
and  MacBride,  after  Gadow.) 


stance.  The 
enemies  of  salamanders  are  supposed  to  be  "  warned  "  by  the 
conspicuous  colors  and  will  not  attack  this  poisonous  species. 

Pronounced  sexual  dimorphism,  i.e.  differences  between  the 
male  and  female  of  the  same  species,  is  exhibited  by  Triton 
cristatus  (Fig.  431),  the  European  crested  newt.  The  male  is 
conspicuously    colored    and 


develops  a  high  serrated 
crest  during  the  breeding 
season. 

Family  Ambystomid^e.  — 
A  common  member  of  this 
family  is  Amby stoma  tigri- 
num  (Fig.  432).  This  species 
occurs  from  New  York  to 
California  and  south  to  cen- 
tral Mexico,  and  reaches  a 
length  of  from  six  to  nine  inches 
with  yellow  spots 


Fig.  432. —The  axolotl  stage  ot  the 
tiger  salamander,  Ambystoma  tigrinum. 
(From  the  Cambridge  Natural  History.) 


It  is  dark  colored  and  marked 
The  larval  form,  called  axolotl,  was  for  a 
long  time  considered  a  separate  species  because  the  external 
gills  persisted  in  the  adult.  Later  it  was  discovered  (1865)  that 
if  forced  to  breathe  air  the  axolotls  would  shed  their  gills  and 


CLASS  AMPHIBIA  517 

become  air-breathing  salamanders  of    the  species  Amby stoma 
tigrinum. 

Family  PLEXHODONTiDiE.  —  All  except  one  species  of  the 
eight  genera  belonging  to  this  family  are  confined  to  America. 
Desmognathus  fusca  (Fig.  433),  the  dusky  salamander,  is  a  species 
four  or  five  inches  long  that  lives  under  stones  and  in  other  dark, 
moist  places.  The  eggs  of  this  species  are  laid  in  two  long 
strings  which  the  female  takes  care  of  in  some  place  of  conceal- 
ment by  winding  them  about  her  body.  Typhlotriton  spelcms 
is  a  blind  species  found  in  a 
cave  in  Missouri.  The  slimy 
salamander,  Plethodon  gluti- 
nosus,  is  common  from  Ohio 
to  the  Gulf  of  Mexico.  It 
gives  off  a  great  quantity  of 
slime  when  irritated.  Autodax 
lugubris    is   an   inhabitant   of 

the     western     United     States.        ^ig.  433'  —  A  lungless  salamander, 

.  •      1     1       •       1  Desmognathus  fuscus ;  female  with  eggs 

It  lays  Its  eggs  m  holes  m  the  in    a    hole    underground.     (From    the 

branches      of      Hve-oak      trees.  Cambridge     Natural     History,     after 

r.      7  7-7-  •  Wilder.) 

Spelerpes  bilmeatus  occurs   in 

the  Atlantic  states.     The  only  European  species  of  the  family 
PlethodontidvE  is  Spelerpes  fuscus. 

Order  3.  Salientia.  —  Most  of  the  Amphibia,  about  nine 
hundred  species  of  frogs  and  toads,  belong  to  this  order.  They 
resemble  one  another  very  closely  and  are  classified  according 
to  the  characteristics  of  certain  internal  structures.  In  North 
America  there  are  seven  families  and  about  fifty-six  species. 
Some  of  them  (toads  and  tree-frogs)  live  on  land,  but  others 
(water  frogs)  spend  a  large  part  of  their  time  in  the  w^ater.  The 
terrestrial  species  possess  only  slightly  webbed  hind  feet  or  no 
webs  at  all.  They  crawl  or  hop  on  land,  burrow  in  the  earth, 
or  climb  trees.  Dark,  moist  hiding  places  are  usually  required, 
and  most  of  them  take  to  water  only  during  the  breeding 
season. 


5l8  COLLEGE  ZOOLOGY 

Suborder  i.  Aglossa.  — There  are  only  a  few  toads  in  this 
suborder;  all  of  them  are  tongueless  and  belong  to  the  family 
Aglossid^.  Pipa  americana  inhabits  the  northern  portion 
of  South  America;  Hymenochirus  bcettgeri  and  Xenopus  IcBvis 
are  confined  to  Africa. 

The  Surinam  toad,  Pipa  americana  (Fig.  434),  has  a  peculiar 
method  of  carrying  its  eggs.  They  are  placed  on  the  back  of 
the  female  during  copulation,  are  held  there  by  a  sticky  secre- 
tion, and  are  gradually  enveloped  by  the  skin.     Within  the 


434.  —  The  Surinam  toad,  Pipa  americana.     (From  Mivart.) 


epidermal  pouches  thus  formed  the  eggs  develop  and  the  tadpole 
stage  is  passed;  then  the  young  toad  escapes  as  an  air-breathing 
terrestrial  animal. 

Suborder  2.  Linguata.  —  Most  of  the  frogs  and  toads  are 
included  in  the  six  families  of  this  suborder. 

Family  i.  Pelobatid^. — There  are  about  twenty  species, 
called  spade-foot  toads,  in  this  family.  One  genus,  Scaphiopus, 
with  four  species,  occurs  in  North  America.  The  spade-foot 
toads  are  burrowing  Amphibia,  and  usually  have  thick  hind  feet 
provided  with  a  sharp  spur  for  digging.     The  spade-foots  of 


CLASS  AMPHIBIA  519 

eastern  North  America  belong  to  the  species  Scaphiopus  hol- 
hrookii.  They  are  seldom  seen  or  heard  except  during  the  breed- 
ing season,  when  they  come  out  of  their  burrows  in  great  numbers 
and  seek  ponds  in  which  to  deposit  their  eggs. 

Family  2.  BuFONiDiE.  —  This  family  includes  over  one 
hundred  species  of  toads,  most  of 'which  belong  to  the  genus 
Bufo.  About  fifteen  species  of  this  genus  have  been  reported 
from  North  America. 

Bufo  americanus,  the  common  toad  of  the  northeastern 
United  States,  possesses  a  rough,  warty  skin,  but  does  not  cause 
the  appearance  of  warts  upon  the  hands  of  those  who  handle 
it,  as  is  often  supposed.  Toads  secrete  a  milky,  poisonous  fluid 
by  means  of  glands  in  the  skin,  which  protects  them  from  many 
animals  that  would  otherwise  be  important  enemies.  During 
the  day  they  remain  concealed  in  some  dark,  damp  place,  but 
at  night  they  sally  forth  and  hop  about,  feeding  upon  worms, 
snails,  and  especially  insects,  which  they  capture  with  their  sticky 
tongue,  as  in  the  case  of  the  frog  (p.  480,  Fig.  410).  The  value 
of  toads  as  destroyers  of  insects  injurious  to  vegetation  is  con- 
siderable. Kirkland  has  estimated  that  one  toad  is  worth 
$19.44  in  a  single  season  because  of  the  cutworms  it  devours. 

During  the  winter  toads  hibernate  in  some  sheltered  nook, 
but  as  soon  as  conditions  are  favorable  in  the  spring  (about 
May  i)  they  emerge  from  their  winter's  home  and  proceed  to 
water  to  deposit  their  eggs.  At  this  time  the  males  utter  their 
sweet,  tremulous  calls.  The  eggs  are  laid  in  long  strings.  They 
develop  very  much  like  those  of  the  frog  (pp.  506-510). 

Family  3.  Hylid^.  —  The  tree-frogs  are  arboreal  amphib- 
ians with  adhesive  discs  on  their  toes  and  fingers  which  usually 
enable  them  to  climb  trees.  They  are  provided  with  large  vocal 
sacs  and  have  a  correspondingly  loud  voice.  Of  the  more  than 
one  hundred  and  eighty  species  belonging  to  the  family,  fifteen 
occur  in  North  America,  and  about  one  hundred  and  thirty  in 
Central  and  South  America.  The  North  American  species 
belong  to  the  genera  Hyla,  Acris,  Chorophilis,  and  Smilisca. 


520 


COLLEGE  ZOOLOGY 


Hyla  versicolor  is  the  common  tree-frog.  It  is  about  two 
inches  long  and  has  the  power  of  slowly  changing  its  color  from 
white  to  stone-gray  or  brown  and  from  white  to  green.  These 
changes  usually  produce  such  a  perfect  harmony  between  the 
frog  and  its  surroundings  that  the  animal  becomes  practically 
invisible.  The  eggs  are  laid  in  May.  They  are  attached  in 
groups  to  plants  at  the  surface  of  the  water. 

Hyla  pickeringii,  the  spring  peeper,  has  the  discs  on  the 
fingers  and  toes  so  small  that  they  are  scarcely  discernible. 


C 


Fig.  435.  —  Brooding  tree-hog,  Nototrema,  female,  from  Venezuela,    la  poslerior 
part  of  trunk  is  opening  of  brood-pouch.     (From  Davenport's  Zoology.) 


Acris  gryllus  is  called  the  cricket-frog.  Chorophilus  nigritus,  the 
swamp  tree-frog,  has  fingers  and  toes  with  mihute  discs.  The 
brooding  tree-frog,  Nototrema  (Fig.  435),  of  Venezuela,  has  a 
pouch  with  an  opening  in  the  hinder  part  of  the  trunk  in  which 
the  eggs  are  placed  and  the  young  are  reared. 

Family  4.  Cystignathid.e.  —  This  family  contains  almost 
as  many  species  (over  one  hundred  and  fifty)  as  the  family 
Hylid^,  but  only  three  species  occur  in  North  America. 
Lithodytes  latrans  and  Syrrophus  marnockii  have  been  recorded; 


CLASS  AMPHIBIA 


521 


from  Texas,  and  Lilhodytes  ricordii  from  Florida.  Most  of  the 
CystignathidcB  occur  in  Mexico  and  Central  and  South  America. 
They  form  a  comparatively  heterogeneous  group  and  are  not 
easily  defined. 

Family  5.  ENGYSTOMATiDiE.  —  The  narrow-mouthed  toads 
as  a  rule  inhabit  the  tropics.  Only  three  of  the  seventy  or  more 
species  are  found  in  the  United  States.  Engystoma  carolinense 
ranges  from  South  Carolina  to  Florida  and  west  to  Texas.  Like 
other  members  of  the  family,  its  head  is  narrow  and  pointed  and 
is  thus  adapted  for  the  capture  of  ants  and  other  small  insects. 

Family  6.  Ranid^.  —  The  true  frogs  occur  in  all  parts  of 
the  globe  except  Australia,  New  Zealand,  and  southern  South 
America.  Only  one  genus,  Rana,  and  about  seventeen  species 
are  found  in  North  America.  Of  these  Rana  pipiens  (pp.  477- 
510)  is  the  most  common. 

Rana  catesbiana,  the  bullfrog,  is  found  all  over  the  United 
States  east  of  the  Rocky  Mountains.  It  is  the  largest  of  the 
family  in  this  country,  often  reaching  a  length  of  six  or  eight 
inches.  Bullfrogs  usually  remain  in  or  near  water.  They 
possess  a  deep,  bass  voice  like  that  of  a  bull,  and  when  a  number 
are  engaged  in  a  nocturnal  serenade  they  can  be  heard  for  a  con- 
siderable distance.  Their  food  consists  of  worms,  insects, 
moUusks,  other  frogs,  young  water-fowl,  etc.  The  eggs  are  de- 
posited in  ponds  from  the  last  of  May  until  July.  The  tadpoles 
do  not  become  frogs  the  first  year  as  do  those  of  the  leopard- 
frog,  but  transform  during  the  second  or  even  the  third  year. 
Bullfrogs  are  worth  from  one  to  four  dollars  per  dozen  in  the 
market,  because  of  the  demand  for  frogs'  legs. 

Rana  clamitans,  the  green  frog,  is  common  in  the  ponds  of 
eastern  North  America.  It  is  little  more  than  half  as  long  as  the 
bullfrog,  from  which  it  may  be  distinguished  by  the  presence  of 
two  glandular  folds  of  skin  along  the  sides  of  the  back. 

Rana  sylvatica,  the  eastern  wood-frog,  is  not  restricted  to 
the  vicinity  of  water,  but  usually  lives  in  damp  woods.  It  is 
found  throughout  the  northeastern  United  States. 


52  2  COLLEGE  ZOOLOGY 

Rana  palustris,  the  pickerel  frog,  inhabits  the  brooks  and 
ponds  of  eastern  North  America,  and  is  often  found  also  in 
fields  and  meadows.     It  reaches  a  length  of  three  inches. 

Suborder  3.  Costata. — The  five  genera 
and  eight  species  of  Salientia  included 
in  this  suborder  all  belong  to  the  single 
family  Discoglossid.e.  Only  one  species 
occurs  in  North  America  ;  this  is  the 
American  discoglossoid  toad,  Ascaphus 
truei,  of  which  only  a  single  specimen 
from  Humptulips,  Washington,  is  known. 
An  interesting  European  species  is  the 
obstetrical  toad,  Alytes  obstetricans  (Fig. 
436).  The  male  of  this  toad  carries  the 
Fig.   436.  —  The    ob-  £„„  strings  with   him  wound   about   his 

stetrical   frog,   Alytes  ob-      ^^        .     ^  .        ,  ,  .      , 

sieiricans;     male,    with  hmd  hmbs,  and  when  the  tadpoles  are 
string   of   eggs.     (From  ready  to  emerge,  takes  to  the  water  and 

Sedgwick's  Zoology,  after 

Claus.)  allows  them  to  escape. 

4.     General  Remarks  on  Amphibia 

Color  and  Color  Change.  —  The  pigments  in  the  skin  of 
Amphibia  are  diffuse  or  granular.  The  latter  are  usually  brown, 
black,  yellow,  or  red  and  are  contained  in  cells  called  chromat- 
ophores.  The  power  of  changing  its  colors  is  possessed  by  most 
Amphibia,  but  especially  by  the  frogs.  These  are  supplied  with 
black  pigment  cells,  interference  cells,  golden  pigment  cells, 
and  sometimes  red  pigment  cells. 

The  black  chromatophores  are  branching  cells  which  may 
spread  out  or  contract,  as  shown  in  Figure  437.  When  ex- 
panded the  pigment  covers  a  larger  area  and  consequently  gives 
the  skin  a  darker  color.  The  yellow  pigment  is  contained  in 
spherical  golden  cells'  The  green  color  results  from  the  re- 
flection of  light  from  granules  of  guanin  in  the  skin  through 
the  golden  cells.  Most  of  the  color  changes  are  due  to  changes 
in  the  concentration  of  the  black  and  yellow  pigments. 


CLASS   AMPHIBIA 


523 


Color  changes  are  brought  about  by  direct  stimulation  of  the 
pigment  cells  or  indirectly  through  the  central  nervous  system. 
Light  is  an  important  stimulus;  it  acts  both  directly  and 
through  the  central  nervous  system.  In  a  bright  light  the  skin 
of  the  frog  becomes  light  in  color,  whereas  in  the  dark  it  changes 
to  a  darker  hue.  Temperature  i^  another  important  factor. 
The  pigment  becomes  more  concentrated  if  the  temperature  is 
raised,  and  the  skin  changes  to  a  lighter  color.     An  expansion 


437 


Pigment  cells  from  the  frog,  in  different  states  of  extension. 
(From  Holmes,  after  Verworn.) 


of  the  pigment  and  a  darker  color  result  from  subjection  to  cold. 
Changes  in  the  circulation,  in  the  moisture  of  the  frog's  habitat, 
and  in  the  chemical  composition  of  the  animal's  environment  affect 
the  chromatophores  and  consequently  produce  changes  in  color. 
In  many  cases  the  color  changes  are  such  as  to  cause  the  frog 
to  resemble  more  closely  its  surroundings,  and  hence  to  conceal  it. 
Regeneration.  —  The  power  of  regenerating  lost  parts  is 
remarkably  well  developed  in  many  Amphibia.  For  example, 
the  hand  of  a  two-year-old  axolotl  was  cut  off,  and  in  twelve  weeks 


524  COLLEGE  ZOOLOGY 

a  complete  hand  was  regenerated  in  its  place  (Barfurth).  Triton 
has  been  observed  to  regenerate  both  limbs  and  tail.  The 
Salientia  are  apparently  unable  to  regenerate  lost  parts  to  any- 
considerable  extent,  except  in  the  early  stages.  As  a  general 
rule,  the  younger  tadpoles  regenerate  limbs  or  tail  more  readily 
than  older  specimens.  There  is  a  distinct  advantage  in  the 
possession  of  the  power  of  regeneration,  since  amphibians  no 
doubt  often  escape  from  their  enemies  with  mutilated  limbs  or 
tail,  but  are  not  seriously  inconvenienced  by  the  loss,  as  new 
parts  rapidly  grow  out. 

Breeding  Habits.  —  Most  Amphibia  are  oviparous,  and  their 
eggs,  as  in  the  leopard- frog,  are  fertihzed  by  the  male  after  ex- 
trusion. In  some  of  the  Caudata  and  in  the  Apoda,  however, 
the  eggs  are  fertilized  before  they  are  laid.  A  few  species  of 
Caudata  bring  forth  their  young  alive;  for  example,  the  fire 
salamander,  Salamandra  maculosa,  of  Europe. 

Several  curious  brooding  habits  have  already  been  referred 
to;  for  example,  the  obstetrical  toad  (p.  522),  the  Surinam  toad 
(p.  518),  and  the  dusky  salamander  (p.  517).  The  "  marsupial  " 
frogs  of  the  genus  Nototrema  should  also  be  mentioned.  They 
have  a  permanent  pouch  on  the  back  in  which  the  eggs  develop. 
These  frogs  belong  to  the  family  Hylidce  and  inhabit  the  tropical 
forest  region  of  South  America. 

Hibernation.  —  Many  Amphibia  bury  themselves  in  the  mud 
at  the  bottom  of  ponds  in  the  autumn,  and  remain  there  in  a 
dormant  condition  until  the  following  spring.  During  this 
period  of  hibernation  the  vital  processes  are  reduced;  no  air 
is  taken  into  the  lungs,  since  all  necessary  respiration  occurs 
through  the  skin;  no  food  is  eaten,  but  the  physiological  activities 
are  carried  on  by  the  use  of  nutriment  stored  in  the  body;  and 
the  temperature  decreases  until  only  slightly  above  that  of  the 
surrounding  medium.  The  temperature  of  all  cold-blooded 
vertebrates  —  cyclostomes,  elasmobranchs,  fish,  amphibians,  and 
reptiles  —  varies  with  the  surrounding  medium.  Frogs  cannot, 
however,  be  entirely  frozen,  as  is  often  stated,  since  death 


CLASS  AMPHIBIA 


52s 


ensues  if  the  heart  is  frozen.  In  warm  countries  many  Amphibia 
seek  a  moist  place  of  concealment  in  which  to  pass  the  hotter 
part  of  the  year.     They  are  said  to  jestiva^-. 

Poisonous  Amphibia.  —  The  poison-glands  of  the  leopard- 
frog  (p.  479)  and  of  the  common  toad  (p.  519)  have  already  been 
mentioned.  Certain  salamanders  ^nd  newts  are  also  provided 
with  poison-glands.  The  poison  acts  upon  the  heart  and  the 
central  nervous  system.  It  has  no  effect  upon  the  skin  of  in- 
dividuals of  the  same  species,  but  if  inoculated  into  the  blood 
it  poisons  even  the  individual  that  produces  it.  As  a  means  of 
defense  the  poison  is  very  effective,  since  an  animal  that  has  once 
felt  the  effects  of  an  encounter  with  a  poisonous  amphibian  will 
not  soon  repeat  the 
experiment.  Some 
of  the  most  poison- 
ous species,  for  ex- 
ample, Salamandra 
maculosa,  are  said 
to  be  warningly 
colored. 

Prehistoric  Am- 
phibia.  —  Two 
orders  of  amphib- 
ians, the  Stego- 
CEPHALiA  and  Mi- 
CROSAURiA  are 
known  only  from 
fossils.  The  Stego- 
CEPHALiA  are  sala- 
mander-like extinct 
animals  (Fig.  438) 
that  lived  in  the 
Carboniferous,  Per- 
mian, and  Triassic  periods.  They  were  probably  fresh-water 
or  terrestrial  creatures.      They  possessed   large,  bony  dermal 


Fig.  438.  —  Stegocephalia.  Branchiosaurus  am- 
Uystomus.  A,  skeleton  of  adult.  B,  restoration  of 
larva  with  branchial  arches.  (From  Sedgwick's 
Zoology,  after  Credner.) 


526  COLLEGE  ZOOLOGY 

plates  on  the  dorsal  surface  of  the  skull  and  often  on  other 
parts  of  the  body.  Some  of  the  Stegocephalia  are  called 
Labyrinthodonts  because  the  dentine  of  their  teeth  is  much 
folded. 

MiCROSAURiA  are  small  extinct  animals  probably  belonging 
to  the  Amphibia,  though  they  are  often  placed  with  the  reptiles. 

The  Economic  Importance  of  the  Amphibia.  —  The  Amphibia 
are  practically  all  beneficial  to  man.  Many  of  them  are  so  rare 
as  to  be  of  little  value,  but  the  frogs  and  toads  are  of  consider- 
able importance.  Frogs  have  been  and  are  now  used  extensively 
for  laboratory  dissections  and  for  physiological  experiments  and 
investigations.  They  seem  in  fact  to  have  been  "  especially 
designed  as  a  subject  for  biological  research." 

Frogs'  legs  are  eagerly  sought  as  an  article  of  food.  New 
York,  Maryland,  Virginia,  Indiana,  Ohio,  Missouri,  and  Cali- 
fornia furnish  the  largest  number  for  market.  Frog  hunters 
obtain  an  annual  price  of  about  $  50,000  for  their  catch.  *'  Frog 
farms  "are  now  carried  on  profitably  in  Wisconsin,  California, 
and  several  other  states.  Small  frogs  are  often  used  as  fish 
bait. 

Frogs  and  toads  are  widely  recognized  as  enemies  of  injurious 
insects.  The  toads  are  of  special  value,  since  they  are  accustomed 
to  live  in  gardens  where  insects  are  most  injurious  (see  p.  519)- 
In  France  the  gardeners  even  buy  toads  to  aid  them  in  keeping 
obnoxious  insects  under  control. 


CHAPTER    XIX 
SUBPHYLUM    VERTEBRATA:     CLASS    V.     REPTILIA 

The  reptiles  constitute  one  of  the  most  interesting,  but  gener- 
ally least  known,  classes  of  the  Vertebrata.  They  are  cold- 
blooded; usually  covered  with  scales  and  frequently  with  bony 
plates;  and  breathe  with  lungs.  The  popular  notion  that  reptiles 
are  slimy  is  erroneous.  Contrary  also  to  general  belief,  very  few 
reptiles,  at  least  in  the  United  States,  are  dangerous  to  man,  but 
the  majority  of  them  are  harmless  and  many  even  beneficial. 
The  reptiles  that  are  living  to-day  are  but  a  remnant  of  vast 
hordes  that  inhabited  the  earth's  surface  in  prehistoric  times. 
In  fact,  of  the  twenty  orders  of  reptiles  now  recognized  by  her- 
petologists,  only  four  possess  living  representatives,  and  one 
of  these  includes  only  one  nearly  exterminated  species  con- 
fined to  New  Zealand.  The  four  orders  of  living  reptiles  are  as 
follows:  — 

Order  i.  Testudinata  (Chelonia).  —  Turtles  and  Tor- 
toises. 

Order  2.  Rhynchocephalia.  —  One  lizard-like  reptile  con- 
fined to  New  Zealand. 

Order  3.  Crocodilini.  —  Crocodiles,  Alligators,  Gavials,  and 
Caimans. 

Order  4.    Squamata.  —  Chameleons,  Lizards,  and  Snakes. 

I.  The  Turtle 

The  turtle  has  been  selected  as  a  type  of  the  Reptilia.  It 
will  not  be  discussed  in  detail,  as  was  the  frog,  but  only  the  more 
important  points  regarding  its  external  and  internal  anatomy 
and  physiology  will  be  mentioned. 

527 


528  COLLEGE  ZOOLOGY 

External  Features.  —  The  shell  of  the  turtle  is  broad  and 
flattened,  and  protects  the  internal  organs.  Even  the  head, 
limbs,  and  tail  can  be  more  or  less  completely  withdrawn  into 
the  shell.  The  neck  is  long  and  very  flexible.  The  head  is 
flattened  dorso-ventrally  and  triangular  in  shape.  The  mouth 
is  large,  but,  instead  of  teeth,  horny  plates  form  the  margin  of 
the  jaws.  The  nostrils,  or  external  nares,  are  placed  close  to- 
gether near  the  anterior  end  of  the  snout.  The  eyes,  situated  one 
on  each  side  of  the  head,  are  each  guarded  by  three  eyelids:  (i) 
a  short,  thick,  opaque  upper  lid;  (2)  a  longer,  thin  lower  lid;  and 
(3)  a  transparent  nictitating  membrane,  which  moves  over  the 
eyeball  from  the  anterior  corner  of  the  eye.  Just  behind  the 
angle  of  the  jaw  on  either  side  is  a  thin  tympanic  membrane.  The 
limhs  usually  possess  five  digits  each;  most  of  the  digits  are  armed 
with  large  claws,  and  connected  one  with  another  by  a  more  or 
less  complete  weh.  The  skin  is  thin  and  smooth  on  the  head, 
but  thick,  tough,  scaly,  and  much  wrinkled  over  the  exposed 
parts  of  the  body. 

Internal  Anatomy  and  Physiology.  —  The  Skeleton.  — 
Since  the  life  of  the  turtle  is  influenced  so  strongly  by  the 
skeleton,  this  system  will  be  described  first. 

The  exoskeleton  (Fig.  439)  consists  of  a  convex  dorsal  portion, 
the  carapace  (c),  and  a  flattened  ventral  portion,  the  plastron 
{Hyp,  Hpp,  Xp) ;  these  are  usually  bound  together  on  each  side 
by  a  bony  bridge  (at  M) .  Both  carapace  and  plastron  are  usually 
covered  by  a  number  of  symmetrically  arranged  epidermal  plates 
iorming  a.  shield ;  the  plates  do  not  correspond  either  in  number 
or  arrangement  to  the  bony  plates  beneath  them.  The  number 
and  shape  of  the  plates  vary  according  to  the  species,  but  are 
usually  constant  in  individuals  of  the  same  species.  The  horny 
shields  of  the  "  Hawk's-bill  Turtle  "  (Fig.  447)  furnish  the  tortoise- 
shell  of  commerce.  Beneath  the  shields  are  a  number  of  bony  plates 
formed  by  the  dermis  and  closely  united  by  sutures  (Fig.  439). 

The  endoskeleton  may,  as  in  other  vertebrates,  be  divided  into 
an   axial   portion   and   an   appendicular    portion.     The    skull 


CLASS   REPTILIA 


529 


(Fig.  440)  is  very  firm.  It  is  devoid  of  teeth.  The  pre- 
maxillae  (pmx),  maxillae  (mx),  and  dentary  bones  possess  sharp 
edges  which  are  covered  with  horn,  and  form  a  beak.  The 
quadrate  bone  (g)  is  stationary;   no  transverse  bone  is  present 


Fig.  439.  —  Skeleton  of  a  turtle,  Cistudo  lutaria,  ventral  aspect;  plastron 
removed  to  one  side,  c,  costal  plates;  co,  coracoid;  e,  entoplastron;  ep,  epi- 
plastron;  /,  fibula;  fe,  femur;  h,  humerus;  hpp,  hypoplastron;  hyp,  hyoplas- 
tron;  jl,  ilium;  js,  ischium;  m,  marginals;  nu,  nuchal;  pb,  pubis;  psc,  precora- 
coid;  py,  suprapygal;  r,  radius;  sc,  scapula;  /,  tibia;  u,  ulna;  xp,  xiphiplastron. 
(From  Zittel.) 

as  in  other  reptiles;  there  is  one  occipital  condyle,  and  only  one 
sphenoidal  bone,  the  basisphenoid  (BSph).  The  supraoccipital 
(so)  has  a  prominent  crest. 

There  are  comparatively  few  vertebrcB  (Fig.  439)  —  usually 
eight  cervical,  ten  thoracic,  two  sacral,  and  a  variable  number  of 
caudal.     The  vertebrae  of  the  neck  move  very  freely  upon  one 


530 


COLLEGE  ZOOLOGY 


another  by  cup  and  ball  joints.  The  thoracic  or  trunk  vertebrae 
bear  ribs  which  are  closely  united  with  the  carapace.  They  lack 
transverse  and  articulating  processes. 

The  pectoral  and  pelvic  girdles  (Fig.  439)  are  peculiarly  situated 
within  instead  of  outside  of  the  ribs.     They  serve,  in  fact,  as 


a»^ 


an  J 


Fig.  440.  —  Skull  of  a  turtle,  Trionyx  gangeticus.  A,  dorsal;  B,  ventral  aspect. 
bo,  basioccipital ;  bsph,  basisphenoid ;  ch,  internal  nares ;  exo,  exoccipital ; 
fr,  frontal;  j,  jugal;  mx,  maxilla;  n,  external  nostril;  op,  opisthotic;  pa,  parietal; 
pi,  palatine;  pmx,  premaxilla;  prf,  prefrontal  -f  nasal;  pro,  prootic;  pif,  post- 
frontal;  q,  quadrate;  quj,  quadratojugal;  s,  supratemporal  fossa;  so,  supra- 
occipital;   sq,  squamosal;   vo,  vomer.     (From  Zittel.) 

braces  to  keep  the  plastron  and  carapace  apart.     The  limbs 
are  almost  typically  pentadactyl. 

The  Digestive  System.  —  Turtles  feed  on  both  plants  and 
animals;  some  are  entirely  vegetarian.  The  animals  preyed 
upon  are  water-fowl,  small  mammals,  and  many  kinds  of  in- 
vertebrates. The  flexible  neck  enables  the  turtle  to  rest  on 
the  bottom  and  reach  out  in  all  directions  for  food.  The  jaws 
of  the  snapping- turtle,  Chelydra  serpentina,  are  powerful  enough 
to  amputate  a  finger,  or  even,  in  large  specimens,  a  hand. 


CLASS  REPTILIA 


531 


The  digestive  organs  are  simple.  The  broad,  soft  tongue  is 
attached  to  the  floor  of  the  mouth  cavity;  it  is  not  protrusible. 
The  two  posterior  nares  are  situated  in  the  anterior  part  of  the 
roof  of  the  mouth.  At  the  base  of  the  tongue  is  a  longitudinal 
slit,  the  glottis,  and  a  short  distance  back  of  the  angle  of  the 
jaw  are  the  openings  of  the  Eustachian  tubes.  The  pharynx 
is  thin-walled  and  very  distensible;  it 
leads  into  the  more  slender  and  thicker- 
walled  oesophagus.  The  stomach  opens 
by  a  pyloric  valve  into  the  small  intes- 
tine; this  is  separated  from  the  large 
intestine  by  the  ileoccecal  valve.  The 
terminal  portion  of  the  alimentary 
canal  is  the  rectum;  it  opens  into  the 
cloaca.    There  is  no  intestinal  caecum. 

The  liver  discharges  bile  into  the  in- 
testine through  the  bile-duct.  Several 
pancreatic  ducts  lead  from  the  pan- 
creas to  the  intestine. 

The  Circulatory  System.  —  The 
heart  (Fig.  441)  consists  of  two  auricles 
(d,  s),  and  a  single  ventricle  which  is 
divided  into  two  by  a  perforated 
septum.  The  venous  blood  from  the 
body  is  carried  by  the  postcaval  vein 


Fig.  441.  —  Heart  and  ar- 
teries of  a  turtle,  Chelydra. 
ad,  right;    as,  left  aortic  arch; 

c,  carotid;    c',   cceliac    artery; 

d,  right    auricle;   d.ao,   dorsal 
.        .                     aorta;  pd,  right;    ps,  left  pul- 

and  the  two  precaval   vems  mtO   the    monary  artery;  s,  left  auricle; 

sinus  venosus   and   thence   into   the  '^^  "^^t;  ss,  left  subclavian 

.  artery.       (From       Sedgwick  s 

right  auncle  {d).      From  here  it  passes    Zoology,  after  Gegenbaur.) 

into  the  right  side  of  the  ventricle, 

and,  when  the  latter  contracts,  is  forced  out  through  the  pul- 
monary artery,  which  sends  a  branch  {pd,  ps)  to  each  lung,  and 
through  the  left  aorta  {as)  which  conveys  blood  to  the  viscera  {c') 
and  into  the  dorsal  aorta  {d.ao). 

The  blood  which  is  purified  in  the  lungs  is  returned  by  the 
pulmonary  veins  to  the  left  auricle  {s)  and  thence  into  the  left 


532 


COLLEGE  ZOOLOGY 


side  of  the  ventricle.  This  blood  is  pumped  out  through  the 
right  aortic  arch  (ad),  which  merges  into  the  dorsal  aorta  {d.ao).' 
Because  the  septum  dividing  the  ventricle  into  two  parts  is 
perforated,    the   blood   that   enters    the   right   aortic   arch   is 

a  mixture  of  purified  blood 
from  the  left  auricle  and 
venous  blood  from  the  right 
auricle. 

There  is  no  renal  portal 
system  in  the  turtle,  but  the 
hepatic  portal  system  shows  an 
advance  in  development  over 
the  condition  as  described  in 
the  frog  (p.  489). 

The  Respiratory  System.  — 
Turtles  breathe  by  means  of 
lungs.  Air  enters  the  mouth 
cavity  by  way  of  the  nasal 
passages.  The  glottis  opens 
into  the  larynx,  through  which 
the  air  passes  into  the  trachea 
or  windpipe.  The  larynx  is 
supported  by  the  hyoid  ap- 
FiG.  442.  —  Cloaca  and  urinogenital  paratus.    The  trachea  divides, 

organs  of  a  turtle,  Chelydra  serpentina.  ,.  ,        ,  ,         ,  , 

e,  c\  blind  sacs  of  cloaca;  cl,  cloaca;  sending  ofte  bronchiis  to  each 

«,  epididymis  and  vas  deferens;  />,  penis,  lung.       The     lungS     are     more 
r,  kidneys;    re,  rectum;    s,  groove  on  i«      1.   j  xv        j.i  r   * 

penis;    /,  testis;    u,  ureter;    ug,  cloacal  Complicated  than  those  of  AM- 

opening  of  bladder;  v,  bladder.     (From  phiBIA.      The    bronchi    branch 
Sedgwick's  Zoology,  after  Gegenbaur.)  ,  .      .  ,      . 

a  number  of  times,  and  the 
lung  cavity  is  broken  up  into  many  spaces,  thus  increasing  the 
respiratory  surface. 

The  shell  of  the  turtle  prevents  the  expansion  and  contraction 
of  the  lungs  by  means  of  abdominal  or  thoracic  muscles.  Air 
is  therefore  drawn  in  and  expelled  partly  by  the  hyoid  apparatus 
and  partly  by  alternately  extending  and  drawing  in  the  neck 


CLASS   REPTILIA 


533 


and  appendages.  The  air  is  thus  pumped  into  the  lungs  or  else 
swallowed. 

Many  aquatic  turtles  possess  a  pair  of  thin-walled  sacs  (Fig. 
442,  cc'),  one  on  either  side  of  the  cloaca  (c/),  which  are  alternately 
filled  with  water  and  emptied  through  the  anus.  They  have 
walls  plentifully  supplied  with  blood-vessels,  and  act  as  auxiliary 
breathing  organs  (compare  sea-cucumber,  p.  206,  and  nymph 
of  dragon-fly,  p.  339). 

The  Urinogenital  Organs  (Fig.  442).  —  Excretion  is  carried 
on  by  the  two  kidneys  (r).  Their  secretions  pass  through  the 
ureters  (u)  into  the  cloaca  (cl),  are  stored  in  the  urinary  bladder 
(t;),  and  then  make  their  exit  {ug)  through  the  anus. 

The  sexes  are  separate.  The  male  organs  are  a  pair  of  testes 
(/)  and  a  pair  of  vasa  deferentia  (e)  through  which  the  spermat- 
ozoa pass  to  the  grooved  copulatory  organ,  or  penis  (p),  at- 
tached to  the  front  wall  of  the  cloaca  (cl).     The  female  organs 

are  a  pair  of  ovaries  and  a      ^ .     ,  ,  ,„,  .^,    ,«.  ,«.   • 

^  T      lot  vKjm  sir  J^  X 

paiir  oi  oviducts ;  the  latter      I         1  \      \7yo  \ 

open  into  the  cloaca. 

Turtles  are  oviparous. 
The  eggs,  which  are  white, 
round  or  oval,  and  covered 
by  a  more  or  less  hardened 
shell,  are  laid  in  the  ground 
a  few  inches  from  the 
surface. 

The  Nervous  System. 
—  The  brain  (Fig.  443)  is 

more  highly  developed  than  in  the  Amphibia.  The  cerebral 
hemispheres  {V H)  are  larger,  and  a  distinction  can  be  made 
between  the  superficial  gray  layer  and  the  central  white  medulla. 
The  cerebellum  (HH)  is  also  larger,  indicating  an  increase  in  the 
power  of  correlating  movements. 

Sense-organs.  —  The  eye  is  small.  It  has  a  round  pupil  and 
an  iris  which  is  usually  dark  in  terrestrial  forms,  but  often 


Fig.  443.  —  Side  view  of  brain  of  a  turtle. 
/,  olfactory  nerve  ;  //,  optic  nerve ;  H,  hypo- 
physis; HE,  cerebellum;  Inj,  infundibulum; 
Lol,  olfactory  lobe;  MR,  optic  lobe;  Nil,  me- 
dulla; R,  spinal  cord;  VH,  cerebral  hemi- 
spheres. (From  Davenport,  after  Wieders- 
heim.) 


534  COLLEGE   ZOOLOGY 

colored  in  aquatic  turtles.  The  sense  of  hearing  is  fairly  well 
developed,  and  turtles  are  easily  frightened  by  noises.  The 
sense  of  smell  enables  the  turtle  to  distinguish  between  various 
kinds  of  food  both  in  and  out  of  the  water.  The  skin  over  many 
parts  of  the  body  is  very  sensitive  to  touch. 

2.  A  Brief   Classification  of  Living  Reptilia^ 

The  four  thousand  or  more  species  of  living  reptiles  may  be 
grouped  into  four  orders:  (i)  the  Testudinata,  containing 
about  two  hundred  and  twenty- five  species  of  turtles  and  tor- 
toises; (2)  the  Rhynchocephalia,  represented  by  a  single  New 
Zealand  species;  (3)  the  Crocodilini,  containing  about  twenty- 
three  species  of  crocodiles,  ga vials,  and  alligators;  and  (4)  the 
Squamata,  containing  about  three  thousand  seven  hundred 
species  of  lizards,  chameleons,  and  snakes.  In  most  cases  the 
orders,  families,  and  subfamilies  of  reptiles  are  indicated  by  means 
of  structural  characters,  such  as  the  position  of  the  teeth,  the 
shape  and  arrangement  of  the  bones  of  the  skull,  and  the  form 
of  the  vertebrae.  Since  these  cannot  be  determined  by  the 
beginning  student,  they  are  mostly  omitted  from  the  following 
paragraphs. 

Order  i.  Testudinata  (Chelonia). — Turtles  and  Tortoises. 
—  Reptiles  with  the  body  incased  in  a  bony  capsule; 
jaws  without  teeth;  quadrate  bone  immovable;  usually 
pentadactyl  appendages. 
Superfamily  i.  Cryptodira.  —  Testudinata  with  the 
carapace  covered  with  horny  shields;  neck  bends  in 
S-shaped  curve  in  a  vertical  plane ;  pelvis  not  fused  with 
the  carapace. 
Family  i.  Chelydrid^.  —  Snapping-turtles.  —  Cryp- 
todira with  small  plastron;  tail  long;  limbs,  neck, 
and  head  large  and  cannot  be  withdrawn  into  shell; 

II  am  indebted  to  Dr.  Alexander  G.  Ruthven  for  the  main  divisions  of  this 
classification. 


CLASS  REPTILIA 


535 


snout    with    hooked     beak.       Examples:     Chelydra^ 
Macrochelys  (Fig.  444). 

Family  2.  Kinosternid^.  —  Musk-  and  Mud -turtles. 
—  Cryptodira  possessing  a  nuchal  plate  with  costi- 
form  processes  underlying  the  marginals  ;  eight 
bones  in  the  plastron.  Examples :  Kinosternofif 
Aromochelys. 

Family  3.  Dermatemydid^.  —  Fresh- water  Turtles 
of  Southern  Mexico  and  Central  America.  Crypto- 
dira with  nuchal  plate  as  in  Kinosternid^e;  nine 
bones  in  plastron.  Examples:  Dermatemys,  Stauroty- 
pus,  Claudius. 

Family  4.  Platysternid^.  —  Cryptodira  without  costi- 
form  processes  on  nuchal  plate.  Examples:  Platy- 
sternum  (a  single  species,  P.  megacephalum,  in  Burma, 
Siam,  and  China). 

Family  5 .  Testudinid^.  —  Tortoises  and  most  Turtles. — 
Cryptodira  without  costiform  processes  on  nuchal 
plate;  lateral  temporal  arch  usually  present;  no 
parieto-squamosal  arch.  Examples:  Testudo  (Fig. 
446),  Chrysemys  (Fig.  445),  Emys. 
Superfamily  2.  Cheloniidea  (Chelonid^  +  Atheca).  — 
Sea-turtles.  —  Marine  Testudinata  with  paddle- 
shaped  limbs. 

Family  i.  Cheloniid^.  —  Four  species  inhabiting  tropical 
and  semitropical  seas  (Fig.  447). 

Family    2.   Dermochelyid^.  —  The    leathery    turtle    of 
tropical  and  semitropical  seas  (Fig.  448). 
Superfamily  3.   Pleurodira.  — Testudinata  with  neck 
bending  laterally;   pelvis  fused  with  the  shell. 

Family  i.  Pelomedusid^.  —  Fresh- water  Turtles. — 
Pleurodira  with  neck  completely  retractile  within 
the  shell;  carapace  without  nuchal  shield;  plastron  of 
eleven  bones.  Examples:  Pelomedusa,  Podocnemis, 
Sternothoerus. 


536  COLLEGE  ZOOLOGY 

Family  2.  Chelydid^.  —  Fresh- water  Turtles.  — 
Pleurodira  with  neck  not  completely  retractile  within 
the  shell ;  plastron  of  nine  bones.  Examples :  Hydras- 
pis,  Emydura. 
Superfamily  4.  Trionychoidea.  —  Testudinata  with 
soft,  leathery  skin,  without  horny  shields. 

Family  i.  Carettochelydid^. — Trionychoidea  with 
paddle-shaped  limbs;  neck  not  retractile.  Example: 
Carettochelys  (one  species  C.  insculpta  from  New 
Guinea.) 

Family  2.  Trionychid^.  —  Soft-shelled  Turtles.  — Tri- 
onychoidea with  digits  broadly  webbed;  head  and 
neck  retractile,  bending  in  vertical  plane.  Examples: 
Trionyx  (Fig.  449),  Emyda. 
Order  2.  Rhynchocephalia.  —  One  genus  of  New  Zealand  lizard- 
like reptiles.  Vertebrae  biconcave,  often  containing 
remains  of  the  notochord;  immovable  quadrate  bone; 
parietal   organ   present.     Example:    Sphenodon   (Fig. 

450)- 
Order  3.    Crocodilini.  —  Crocodiles,    Alligators,    Ga vials, 

and    Caimans. — Reptiles    with   proccelous  vertebrae; 

nostril  single,  at  end  of  snout;    anterior  appendages 

with  five  digits,  posterior  with  four  and  traces  of  a 

fifth;  anal  opening  a  longitudinal  slit. 
Family    i.   Gavialid^.  —  Ga  vials.  —  Crocodilini    with 

long,  slender  snout.     Example:    Gavialis  (Fig.  451). 
Family  2.   Crocodilid^.     Crocodiles,  Alligators,  and 

Caimans.  —  Crocodilini  with  broad,  rounded  snout. 

Examples:    Crocodilus,  Alligator,  Caiman  (Fig.  451). 
Order  4.    Squamata.  —  Chameleons,  Lizards,  and  Snakes. — 

Reptiles  usually  with  horny  epidermal  scales ;  vertebrae 

usually  proccelous;    quadrate  bones  movable. 
Suborder    i.    Rhiptoglossi.  —  Chameleons.  —  Squamata 

with    body    laterally    compressed;     tail    prehensile; 

tongue   vermiform,  projectile;    well-developed   limbs; 


CLASS   REPTILIA  537 

digits  in  groups  of  two  and  three,  for  grasping   (see 
Fig.  452). 

Family  i.  Cham^leontid.^.  —  Chameleons.  —  With 
characters  of  the  suborder.  Examples:  Chamcdeon 
(Fig.  452),  Brookesia,  Rhampholeon. 
Suborder  2 .  S auria  (Lacertilia)  .  —  Lizards.  —  S  quamata 
with  transverse  anal  opening ;  paired  copulatory  organs ; 
at  least  a  vestige  of  a  pectoral  arch;  usually  well- 
developed  limbs ;  rami  of  lower  jaw  united.  (Only  ten 
of  the  twenty  families  are  listed  below.) 

Family  i .  Geckonid^.  —  Gecko. — S auria  with  four  legs ; 
eyes  usually  without  movable  lids;  tongue  protrusible; 
many  with  adhesive  digits  for  climbing.  Examples: 
Gecko  (Fig.  453),  Gymnodactylus ,  Sphcerodactylus. 

Family  2.  Agamid^e.  —  Old-world  Lizards.  —  S auria 
with  well-developed  limbs;  eyes  with  complete  lids; 
tongue  broad  and  short;  teeth  usually  differentiated 
into  incisors,  canines,  and  molars  (heterodont) ,  and 
always  situated  on  the  edge  of  the  jaw  (acrodont). 
Examples:  Draco  (Fig.  454),  Gonycephalus,  Calotes. 

Family  3.  Iguanid^.  —  New-world  Lizards. — Sauria 
resembling  Agamid^,  but  usually  with  teeth  similar 
(homodont)  and  fastened  in  a  groove  (pleurodont). 
Examples:  Anolis,  Sceloporus,  Phrynosoma  (Fig.  457), 
Iguana  (Fig.  456). 

Family  4.  Anguid^e.  —  Old  and  New-world  Lizards. 
Sauria  with  teeth  in  a  groove;  anterior  part  of  tongue 
thin,  and  retractile  into  posterior  part;  limbs  present 
or  absent;  body  protected  by  bony  plates. 

Family  5.  Helodermatid^.  —  Beaded  Lizards.  —  Sauria 
with  grooved  teeth ;  poisonous;  tongue.bifid, protractile; 
limbs  short  but  strong.   Examples :  Heloderma  (Fig.  459) . 

Family  6.  Varanid/E.  —  Monitors.  —  Sauria  with  tongue 
long,  smooth,  deeply  bifid  and  retractile;  tail  long; 
limbs  well  developed.     Example:    Varanus. 


538  COLLEGE  ZOOLOGY 

Family  7.  Teiid^.  —  New- world  Lizards.  —  Sauria  with 
tongue  long  and  bifid,  with  scale-like  papillae;  limbs 
normal  or  reduced.  Examples:  Ameiva,  Cnemido- 
phorus. 

Family  8.  AMPHiSBiENiDiE. — Worm  Lizards. — Vermi- 
form Sauria  with  short  tail;  limbs  absent  (except  in 
Chirotes);  girdles  reduced;  eyes  and  ears  concealed; 
skin  divided  into  regulp,r  rings.  Examples:  Amphis- 
b(Bna,  MonopelHs,  Lepidosternon. 

Family  9.  Lacertid^e.  —  Typical  Old-world  Lizards.  — 
Sauria  with  well-developed,  pentadactyl  limbs,  with 
sharp  claws;  tail  long,  brittle;  tongue  long,  bifid, 
with  papillae  or  folds.  Examples:  Lacerta^  Acantho- 
dactylus,  Eremias. 

Family  10.  SciNCiDiE.  —  Skinks.  —  Sauria  with  tongue 
scaly,  and  only  slightly  nicked;  limbs  may  be  reduced 
or  absent ;  strongly  developed  bony  plates  on  head  and 
body.  Examples:  Mabuia,  Lygosoma,  Eumeces. 
Suborder  3.  Serpentes  (Ophidia).  —  Snakes. — Elongated 
Squamata  without  hmbs;  anal  opening  transverse; 
copulatory  organs  paired;  without  movable  eyelids, 
tympanic  cavity,  urinary  bladder  and  pectoral  arch; 
rami  of  lower  jaw  connected  by  ligament.  (Four  of 
the  nine  families  and  several  of  the  subfamilies  are  not 
.  included  in  the  following  list.) 

Family  i.  TYPHLOPiDiE. — Burrowing  Snakes. — Ser- 
pentes with  reduced  eyes  covered  by  scales;  without 
teeth  in  lower  jaw;  pelvis  represented  by  vestiges. 
Examples:    Typhlops,  Helminthophis. 

Family  2.  Glauconiidje. — Burrowing  SnakeS. — Ser- 
pentes resembling  the  Typhlopid^e  ;  lower  jaw  toothed ; 
vestiges  of  pelvis  and  hind  limbs.  Examples:  Glau- 
coma ^  Anomalepis. 

Family  3.  Boid^. — Pythons  and  Boas.  —  Serpentes 
usually  large,  with  vestiges  of  pelvis  and  .hind  limbs; 


Class  reptilia  539 

ventral  scales  transversely  enlarged;  eyes  functional 

and  free. 
Subfamily  I.   Pythonin-^:.     Pythons. — Examples:  L(7x- 

ocemus,  Liasis,  Python  (Fig.  460). 
Subfamily    2.   BoiNiE. — Boas. — Examples:    Epicrates, 

Boa  J    Ungalia. 
Family    4.     Colubrid^.  —  Harmless     and     Poisonous 

Snakes.  —  Serpentes  with  facial  bones  movable;  both 

jaws  toothed. 
Series  A.   Aglypha.  —  Colubrid^  with  solid  teeth,  not  grooved 

or  tubular.     Non-venomous. 
Subfamily       i.       Colubrin^.  —  Typical    Harmless 

Snakes. — Examples:    Thamnophis  (Fig.  461),  Zawe- 

nis,  Elaphe. 
Series  B.   Opisthoglypha.  —  Colubrid^  with  grooved  fangs  in 

the  rear  of  the  upper  jaw.     Venomous. 
Subfamily    2.   Homalopsin^e.  —  River    Snakes.  —  Ex- 
amples:   Hypsirhina,  Homalopsis. 
Subfamily  3.  Dipsadomorphin^e. — ^ Examples:  Tantilla, 

Philodryas,  Oxyrhopus. 
Series  C.   Proteroglypha.  —  Colubrid^   with   fangs   in  the 

front  of  the  upper  jaw.     Venomous. 
Subfamily  4.     Hydrin^.  —  Sea-snakes.  —  Examples : 

Hydrophis,  Distira,  Platurus. 
Subfamily  5.  Elapin^.  — Cobras  and  Coral-snakes.  — 

Examples:    Naja  (Fig.  462),  Elaps,  Denisonia. 
Family  5.  Viperid^e.  —  Thick-bodied  Poisonous  Snakes. 

—  Poisonous  Serpentes  with  a  pair  of  large  perforated 

fangs. 
Subfamily   i.   Viperin^. — True  Vipers. — Examples: 

Vipera,  Atractaspis. 
Subfamily  2.    Crotalin^.  —  Pit- vipers.  —  Examples: 

Crotalus  (Fig.  466),   Agkistrodon  (Figs.  463  and  464), 

Lachesis. 


540 


COLLEGE  ZOOLOGY 


3.  Review  of  the  Orders  and  Families  of  Living  Reptiles 

Order  I.  Testudinata. — Turtles  and  Tortoises. — The 
Testudinata  are  reptiles  with  a  short,  stout  body  provided  with 
a  shell  —  a  structural  feature  that  distinguishes  them  from  other 
animals  as  effectively  as  wings  and  feathers  do  the  birds.  They 
are  without  teeth;  the  neck  is  very  flexible;  and  the  limbs  are 
fitted  for  creeping,  running,  or  swimming.  The  position  of  the 
pectoral  and  pelvic  girdles  within  instead  of  outside  of  the  ribs  is 
peculiar.  They  all  deposit  eggs  in  sand  or  earth,  where  they  are 
left  to  develop.  Some  turtles  are  carnivorous;  others  are 
herbivorous. 

America  is  the  richest  of  all  countries  in  Testudinata.  Three 
of  the  eleven  families  —  Dermatemydid^,  Kinosternid^, 
and  Chelydrid^e  —  are  now  restricted  to  North  and  Central 
America.     Most  of  the  land  and  fresh-water  turtles  hibernate 

in  the  earth  during 
the  winter,  but  in 
warmer  countries 
they  sleep  during 
the  hotter  months 
(aestivate). 

Family  Chely- 
drid^.— Snapping- 
TURTLES.  —  Only 
three  species  belong 
to  this  family. 
Chelydra  serpen- 
tina,  the   common 


Fig. 


444.  —  The  alligator  turtle,  Macrochelys 
lacertina.     (From  Gadow.) 


snapping-turtle,  in- 
habits fresh-water 
ponds  and  streams  of  North  America  east  of  the  Rocky  Moun- 
tains and  southward  to  Ecuador.  It  is  a  voracious,  carnivorous 
animal  feeding  on  fish,  frogs,  water-fowl,  etc.,  and  does  not 
hesitate  to  attack  man  with  its  formidable  beak,  often  inflicting 


CLASS  REPTILIA  541 

severe  wounds.  The  plastron  is  very  small  and  offers  little 
protection  for  the  body.  Chelydra  rossignonii  is  a  native  of 
Mexico  and  Guatemala,  differing  only  slightly  from  C.  serpentina. 

The  alligator  snapping- turtle,  Macrochelys  lacertina  (Fig.  444), 
lives  in  the  streams  of  the  southeastern  United  States.  It  is  the 
largest  North  American  turtle,  attaining  a  weight  of  one  hundred 
and  forty  pounds  and  a  length  of  shell  of  twenty-eight  inches. 
It  has  "  a  head  as  large  as  that  of  a  bull- terrier  and  jaws  that  can 
chop  up  an  ordinary  broom  handle,"  and  a  bad  temper  as  well. 
The  flesh  of  the  snapping-turtle  is  a  regular  article  of  food  in 
certain  localities. 

Family  Kinosternid^. — Musk-  and  Mud-turtles.  — These 
are  all  confined  to  America.  There  are  three  species  of  musk- 
turtles  belonging  to  the  genus  Aromochelys,  and  eleven  species 
of  mud-turtles  of  the  genus  Kinosternon. 

The  common  musk-turtle,  Aromochelys  odoratus,  is  an  inhabit- 
ant of  the  muddy  streams  of  the  eastern  United  States.  It  has 
a  carapace  three  or  four  inches  long,  a  large  head,  and  broadly 
webbed  feet.  It  is  voracious  and  carnivorous.  The  disagree- 
able odor  it  emits  when  captured  has  given  it  its  name. 

The  common  mud- turtle,  Kinosternon  pennsylvanicum,  shares 
the  habitat  of  the  musk- turtle,  and  resembles  the  latter  in  size 
and  in  habits. 

Family  Testudinid^.  —  Turtles,  Terrapins,  and  Tor- 
toises. —  There  are  twenty- two  genera  and  about  one  hundred 
and  ten  species  in  this  family.  Space  will  permit  a  brief  dis- 
cussion of  only  six  or  eight  of  these. 

The  painted  terrapin,  Chrysemys  picta  (Fig.  445),  inhabits 
the  ponds  and  sluggish  rivers  of  eastern  North  America.  It 
loves  to  sun  itself  upon  a  log  or  protruding  rock,  from  which  it 
slides  off  into  the  water  when  disturbed.  It  feeds  on  aquatic 
insects,  tadpoles,  fishes,  and  water-plants.  The  shells  of  the 
painted  terrapin  are  beautifully  colored  and  are  often  carefully 
cleaned  and  then  varnished,  in  which  condition  they  make  very 
pretty  ornaments. 


542 


COLLEGE  ZOOLOGY 


The  diamond-back  terrapin,  Malacoclemmys  palustris,  is 
famous  as  an  article  of  food.  It  lives  in  the  salt  marshes  of  the 
Atlantic  coast.  Persistent  persecution  by  market  hunters  has 
caused  a  great  decrease  in  the  number  of  these  animals  and  a 
corresponding  increase  in  their  value. 
The  price  has  risen  from  twenty-five 
cents  for  a  large  specimen  to  seventy 
dollars  per  dozen  for  small  ones  (Horna- 
day). 

The  spotted  or  pond  turtle,  Clemmys 
guttatus,  is  abundant  in  the  ponds, 
marshes,  and  streams  of  the  eastern 
United  States.  Like  the  painted  terra- 
pin, they  may  often  be  seen  in  groups 
sunning  themselves  on  floating  logs. 
They  feed  on  dead  fish,  insect  larvae, 
and  probably  water-plants.  The  western 
pond  turtle,  Clemmys  marmorata,  is  the 
only  common  fresh-water  turtle  along 
the  Pacific  coast. 
Blanding's  turtle,  Emys  blandingii,  is  a  fresh-water  form 
common  in  the  Middle  States.  Its  carapace  measures  about 
eight  inches  in  length  and  its  plastron  is  hinged  so  that  it  can  be 
partially  closed.  This  species  is  not  as  aquatic  as  the  Testu- 
DiNiDiE  already  described,  but  is  often  found  wandering  about 
on  wet  ground.  Unlike  the  more  aquatic  turtles,  it  can  eat  out 
of  water.     Emys  orbicularis  is  the  European  pond  turtle. 

Terrapene  Carolina  is  the  common  box  turtle.  The  plastron  of 
this  species,  and  of  the  five  other  species  belonging  to  the  genus 
Terrapene,  is  hinged  transversely  near  the  center  so  that  the  shell 
can  be  closed  completely  when  the  animal  is  in  danger.  Terrapene 
Carolina  has  a  highly  arched  carapace  about  five  inches  in  length. 
It  occurs  in  the  Northeastern  states  and  is  terrestrial  in  habits, 
living  in  dry  woods  and  feeding  on  berries,  tender  shoots,  earth- 
worms, and  insects. 


^.TTft'»P'"i'i 


Fig.  445.  —  The  painted 
terrapin,  Chrysemys  picta. 
(From  Gadow.) 


CLASS   REPTILIA  543 

The  gopher  tortoise,  Gopherus  polyphemus,  Hves  in  burrows  in 
dry,  sandy  areas  of  the  southeastern  United  States.  It  is  a  slow- 
moving,  herbivorous,  terrestrial  animal.  The  common  Greek 
tortoise  of  southern  Europe  belongs  to  the  genus  Testudo. 

The  giant  tortoises  (Fig.  446)  are  interesting  not  only  because 
of  their  great  size,  but  also  becausc'they  are  living  representatives 
of  the  fauna  of  past  ages.  Six  species  inhabit  the  Galapagos 
Islands  off  the  west  coast  of  South  America;  four  species  occur 
in  the  Aldabra  Islands  of  the 
Indian  Ocean,  and  four  species 
inhabit  the  Mauritius-Rodri- 
guez Group  of  islands.  Some 
of  those  captured  on  the  Galap- 
agos Islands  weigh  over  three 
hundred  pounds  and  are  prob- 
ably over  four  hundred  years 
old.  These  giant  tortoises  "* 
live  on  cacti,  leaves,  berries, 
and  coarse  grass.     They  have     ^'"^"•^•'"''"^ 

,  ^    1    f        f       1  1     Fig.  446.  —  A  giant  tortoise,   Testudo 

been  persecuted  for  food  and  abingdoni.    (From  Gadow.) 

for  scientific  purposes  so  per- 
sistently that  extermination  in  a  wild  state  seems  certain  within 
a  few  years. 

Family  Cheloniidea.  —  Sea-turtles.  —  These  are  the  giant 
water  turtles.  They  inhabit  tropical  and  semitropical  seas  and 
come  to  land  only  to  lay  their  eggs  on  sandy  beaches.  Their 
Kmbs  are  modified  as  paddles  for  swimming.  The  two  species 
of  loggerhead  turtles  belong  to  the  gGuus'  Thalassochelys.  Some 
indi\dduals  have  a  carapace  four  feet  in  length  and  weigh  five 
hundred  pounds. 

The  green  turtle,  Chelonia  mydas,  so  called  because  of  the 
green  color  of  its  fat,  is  almost  as  large  as  the  loggerhead.  It 
is  famous  as  an  article  of  food,  and  is  common  in  the  markets  of 
the  large  cities  of  the  eastern  United  States.  It  feeds  largely  on 
aquatic  vegetation  and  probably  eats  fish,  and  other  animals  also. 


544 


COLLEGE  ZOOLOGY 


.msm 


Fig.  447.  —  The  hawk's-bill  turtle,  Chdoniaimhricata, 
young.     (From  Gadow.) 


The  hawk's-bill   or  tortoise-shell  turtle,   Chelonia  imbricata 
(Fig.  447),  has  the  shields  of  its  carapace  arranged  like  the 

shingles  on  a  roof. 
These  shields,  of 
which  a  large  speci- 
men yields  about  eight 
pounds,  are  the  "  tor- 
toise "  shell  of  com- 
merce. The  shields 
are  detached  either 
after  the  turtles  have 
been  killed  and  im- 
mersed in  boiling  water 
m  or  after  the  li\dng 
animals  have  been 
suspended  over  a  fire. 
In  the  latter  case  the 
animals  are  liberated 
and  allowed  to  regenerate  a  new  covering  of  shields.  The  re- 
generated shields,  however,  are  not,  as  supposed,  of  com_mercial 
value.  Hawk's-bill  turtles  are  smaller 
than  the  logger-head  and  green  turtles, 
reaching  a  weight  of  about  thirty 
pounds  and  a  carapace  length  of 
thirty  inches.  They  are  carnivorous, 
feeding  largely  on  fish  and  mollusks. 

Family  DERMOCHELYiDyE. — Leath- 
ery Turtle. — The  single  species  of 
this  family,  Sphargis  coriacea  (Fig.  448) , 
is  the  largest  of  all  living  turtles,  some- 
times attaining  a  weight  of  a  thousand 
pounds.  It  has  a  leathery  covering 
over  the  shell  instead  of  horny  shields. 
It  inhabits  tropical  and  semitropical 
seas  and  goes  to  land  only  to  deposit 


turtle, 
young. 


-  The  leathery 
Sphargis  coriacea, 
(From  Gadow.) 


CLASS  REPTILIA  545 

its  eggs.  The  limbs  are  modified  as  flippers  for  swimming. 
The  flesh  is  not  used  for  food. 

Family  Chelydid^.  —  This  is  one  of  the  families  of  turtles, 
the  members  of  which  bend  the  neck  laterally.  They  are  all 
fresh-water,  semiaquatic  species  and  are  found  in  South  America, 
Australia,  and  New  Guinea.         ' 

Family  Trionychid^e.  —  Soft-shelled  Turtles.  —  The  six 
genera  and  about  twenty-four  species  belonging  to  this  family 
inhabit  fresh- water  ponds  and  streams  in  various  parts  of  North 
America,  Africa,  Asia,  and  the  East  Indies.  The  four  species 
occurring  in  North  America  are  members  of  the  genus  Trionyx. 
They  are  thoroughly  aquatic  and  have  large,  strongly  webbed 
feet.  The  body  is  flat;  the-  neck  is  long  and  very  flexible; 
the  nose  terminates  in  a  small  proboscis;  and  the  shell  is  leathery 
without  shields,  and  with  only  a  few  scattered  bones. 

Trionyx  ferox  (Fig.  449)  is  the  southern  soft-shelled  turtle 
of  North  America,  occurring  in  muddy-bottomed  streams  and 


Fig.  449.  —  The  soft-shelled  turtle,   Trionyx  ferox.     (From  Gadow.) 

ponds  of  Georgia,  Florida,  and  Louisiana.  In  the  Central 
United  States  the  common  species  is  the  spiny  soft-shelled  turtle, 
Trionyx  spmifer.     These  turtles  are  voracious  and  carnivorous, 


546 


COLLEGE  ZOOLOGY 


feeding  on  fish,  frogs,  young  water-fowl,  and  mollusks.  When 
attacked  they  are  very  vicious.  The  shell  as  well  as  other 
parts  of  the  animals  are  used  as  food  and  are  regularly  sold 
in  the  markets. 

Order  2.  Rhynchocephalia.  —  There  is  only  a  single  living 
representative  of  this  order  —  Sphenodon  punctatum  (Fig.  450). 
This  reptile,  which  formerly  inhabited  all  of  the  main  islands  of 
New  Zealand,  is  now  restricted  to  some  small  islets  in  the  Bay 


-  ..'?#li*#^^i^5^y%' 


Fig.  450.  —  Sphenodon  punctatum.     (From  Gadow.) 


of  Plenty,  and  will  probably  soon  be  entirely  exterminated.  It 
is  about  two  feet  long  and  resembles  a  lizard  in  form.  It  lives 
in  burrows,  is  nocturnal,  and  feeds  on  other  live  animals. 

One  of  its  most  striking  peculiarities  is  the  presence  of  a  well- 
developed  parietal  organ  or  pineal  eye  in  the  roof  of  the  cranium, 
which  has  all  the  characters  of  a  simple  eye.  It  is  also  the  only 
reptile  without  a  copulatory  organ.  Numerous  skeletal  char- 
acteristics are  like  those  possessed  by  some  of  the  oldest  fossil 
reptiles,  and  the  ancestors  of  living  reptiles  were  apparently 
much  like  this  queer  relic  of  past  ages. 


CLASS   REPTILIA 


547 


Order  3.  Crocodilini.  —  Crocodiles,  Alligators,  Ga vials, 
and  Caimans  (Fig.  451).  These  reptiles  are  lizard-like  in  form, 
but  have  the  jaws  extended  into  a  long  snout.  The  nostrils 
are  at  the  end  of  the  snout  and  the  eyes  protrude  from  the  head 
so  that  the  crocodilians  can  float  at  the  surface  with  only  these 
parts  above  the  water.  The  skin  is  thick  and  leathery,  covered 
with  horny  epidermal  scales,  and  with  dorsal,  and  sometimes 


Fig.  451.  —  Crocodilini.  A  loUf,  .— ^^LcvI  gavial  {Ga-cialis  ^angdicus)  on  top 
of  an  American  crocodile  {Crocodilus  americaniis) .  A  Nile  crocodile  {Crocodilus 
niloticus)  in  the  foreground.  A  "  mugger "  {Crocodilus  paluslris)  in  the  right 
upper  corner.     Notice  peculiar  floating  attitude  of  young.      (From  Gadow.) 


ventral  bony  plates  somewhat  like  those  in  the  shell  of  the 
turtles.  The  nostrils  and  ears  are  provided  with  valves  and  are 
closed  when  the  animal  is  under  water. 

The  limbs  are  well  developed.  There  are  five  digits  on  the 
fore  limbs  and  four  more  or  less  webbed  digits  on  the  hind  limbs. 
The  tail  is  a  laterally  compressed  swimming  organ.  The  anus 
is  a  longitudinal  slit.  Two  pairs  of  musk  glands  are  present,  — 
one  on  the  throat,  and  one  in  the  cloaca. 

Some  of  the  peculiarities  of  the  internal,  structures  are  as 


548  COLLEGE  ZOOLOGY 

follows.  The  vertebrae  are  mostly  procoelous;  all  of  the  cervi- 
cal and  trunk  vertebrae  and  some  of  the  caudal  vertebrae  bear 
ribs,  a  number  of  which  are  attached  by  two  heads;  there  is  a 
sternum,  but  no  clavicles;  the  teeth  are  conical  and  are  shed  at 
intervals,  being  replaced  by  others  which  grow  up  beneath 
them;  they  are  set  in  sockets  (thecodont)  on  the  premaxillae, 
maxillae,  and  dentary  bones;  the  tongue  is  flat  and  non-pro- 
trusible,  but  can  be  raised  and  lowered,  serving  as  a  valve  to 
prevent  water  from  entering  the  oesophagus  when  the  mouth 
is  opened  under  water;  palatal  folds  separate  the  upper  air- 
passage  from  the  lower  food  passage;  there  are  no  salivary 
glands,  no  intestinal  caecum,  and  no  bladder;  the  lungs  are 
partitioned  off  from  the  rest  of  the  organs  in  the  body-cavity 
by  a  membrane  which  assists  in  respiration  and  is  analogous 
to  the  diaphragm  of  mammals;  the  ventricle  of  the  heart  is 
completely  divided  into  two  by  a  septum,  whereas  that  of  other 
reptiles  is  only  partially  divided;  the  cerebellum  is  more  highly 
developed  than  in  the  other  reptiles;  the  penis  resembles  that 
of  the  turtles  (see  Fig.  442). 

Family  Gavialid^.  —  Two  of  the  twenty-one  species  of 
living  Crocodilini  belong  to  this  family.  Gavialis  gangeticus^ 
the  Indian  gavial,  lives  in  northern  India,  and  Tomistoma  schle- 
geli,  the  Malayan  gavial,  lives  in  Borneo  and  Sumatra.  The 
Indian  gavial  (Fig.  451)  reaches  a  length  of  twenty  feet  or  more, 
and  has  a  very  long,  slender  snout.  It  inhabits  the  Ganges 
and  Brahmaputra  rivers  and  their  territories.  The  food  of 
the  gavial  consists  principally  of  fish;  man  is  seldom  if  ever 
attacked. 

Family  Crocodilid.e.  —  This  family  contains  four  genera  — 
Crocodilus,  Osteolosmus,  Caiman,  and  Alligator.  Crocodilus 
americanus,  the  American  crocodile  (Fig.  451),  is  an  inhabitant 
of  Florida,  Mexico,  and  Central  and  South  America.  It  has 
a  triangular  head  becoming  very  narrow  toward  the  snout.  It 
attains  a  length  of  fourteen  feet.  In  Florida  the  crocodile  digs 
burrows  in  the  bank  in  which  to  hide ;  the  openings  are  entirely 


CLASS   REPTILIA 


549 


or  partly  under  water.  The  American  crocodile  is  not  dangerous 
to  man. 

The  African  crocodile,  Crocodilus  niloticus  (Fig.  451),  is  one 
of  the  few  man-eating  species,  and  has  probably  destroyed  more 
human  beings  than  any  other  kind  of  wild  animal  in  the  dark 
continent.  Formerly  it  was  held  *^cred  by  the  Egyptians,  and 
many  specimens  were  preserved  as  mummies. 

The  other  nine  species  of  the  genus  Crocodilus  live  in  various 
parts  of  the  world  —  C.  intermedius,  the  Orinoco  crocodile,  in 
Venezuela ;  C.  rhomhifer,  the  Cuban  crocodile,  in  Cuba ; 
C.  moreletti,  the  Guatemala  crocodile,  in  Guatemala  and 
Honduras;  and  the  others  in  Africa,  Australia,  Siam,  Java, 
India,  Malaysia,  or  Madagascar.  The  salt-water  crocodile, 
C.  porosus,  which  occurs  in  India  and  Malaysia,  is  a  man- 
eating  species. 

The  five  species  of  caimans  occur  in  Central  and  tropical 
South  America.  The  spectacled  caiman.  Caiman  sclerops, 
ranges  from  southern  Mexico  southward  into  Argentina.  It 
reaches  a  length  of  eight  feet.  The  largest  American  crocodile 
is  the  black  caiman.  Caiman  niger,  of  the  upper  Amazon. 
Some  of  these  animals  are  said  to  be  twenty  feet  long. 

There  are  two  species  of  the  genus  Alligator;  the  American 
alligator,  A.  mississippiensis,  inhabits  the  southeastern  United 
States;  and  the  Chinese  alligator,  A.  sinensis,  is  found  only  in 
China.  The  American  alligator  has  a  broad,  blunt  snout,  and 
is  stouter,  less  active,  and  less  vicious  than  the  crocodiles.  It 
attains  a  length  of  sixteen  feet,  but  most  of  the  large  specimens 
have  been  killed  for  their  hides,  so  that  probably  none  now  exist 
in  the  wild  state  over  twelve  feet  long.  The  habits  of  the  alli- 
gator are  similar  to  those  of  the  crocodile.  The  nest  is  a  moimd 
of  earth  and  rotting  vegetation.  From  twenty  to  forty  eggs  are 
deposited  in  this  nest  and  left  to  hatch  without  any  assistance 
from  the  parents. 

The  Chinese  alligator  inhabits  the  Yangtse-Kiang  River  of 
China.     It  is  only  six  feet  long. 


550 


COLLEGE  ZOOLOGY 


Order  4.  Squamata.  —  Chameleons,  Lizards,  and  Snakes. 
These  animals  resemble  one  another  rather  closely  in  structure. 
They  are  all  protected  by  horny,  epidermal  scales,  and  often  by 
dermal  plates  of  bone.  The  horny  layer  of  the  skin  is  cast  off 
periodically.  The  anus  is  a  transverse  slit  and  there  are  two 
copulatory  organs  in  the  male.  The  legless  lizards  and  snakes 
have  undoubtedly  evolved  from  ancestors  with  limbs.  In  all 
the  living  Squamata  the  limbs,  when  present,  are  adapted  for 
walking  on  land. 

Suborder  i.  Rhiptoglossi.  —  Chameleons. — A  number  of 
different  kinds  of  Squamata  are  called  Chameleons,  but  the  true 

Chameleons  be- 
long to  the  single 
family  Cham^le- 
ONTiD^  of  the 
suborder  Rhipto- 
glossi. There  are 
fifty  species,  all  of 
which  live  in  Africa 
and  Madagascar; 
two  of  them  also 
occur  in  Spain, 
India,  and  Ceylon. 
The  three  genera 
are  Chamceleon 
(Fig.  452)  with 
forty-five  species,  Brookesia  with  three  species,  and  Rham- 
pholeon  with  two  species. 

The  Chameleons  differ  from  other  Squamata  both  in  external 
features  and  in  internal  structure.  The  body  is  laterally  com- 
pressed; the  tail  is  prehensile,  is  not  brittle,  and  cannot  be  re- 
generated if  lost;  the  limbs  are  long  and  slender,  and  the  digits 
are  grouped  so  that  two  are  permanently  opposed  to  the  other 
three;  the  head  usually  bears  a  prominent  crest;  no  tympanum 
and  t}mipanic  cavity  are  present;  the  pectoral  girdle  lacks  clavicles 


Fig.  452.  —  The  chameleon,  Chamoeleon  vulgaris. 
(From  Gadow.) 


CLASS   REPTILIA 


551 


and  interclavicles;  the  eyelids  are  united  into  a  single  fold  with 
a  small  central  opening;  the  eyes  are  moved  separately,  causing 
the  animal  to  squint.  The  tongue  is  club-shaped  and  covered 
by  a  sticky  secretion;  it  can  be  projected  by  muscles  and  by 
the  inflow  of  blood  to  a  distance  of  over  six  inches,  and  is  used 
like  that  of  the  frog  (p.  480,  Fig.  410)  for  capturing  live  insects 
which  constitute  its  entire  food.  The  skin  is  covered  with 
granules;  it  is  shed  several  times  a  year,  coming  off  in  large 
flakes  when  the  body  is  rubbed  against  stones  or  the  limbs  of 
trees. 

One  of  the  features  that  has  made  the  chameleons  famous  is 
the  power  of  rapidly  changing  their  colors.  This  is  brought 
about  with  the  aid  of  chromatophores  (see  p.  522)  and  is  ap- 
parently partly  under  the  control  of  the  animal  and  partly  due 
to  external  stimuli,  such  as  light  and  temperature. 

A  few  chameleons  are  viviparous,  but  most  of  them  deposit 
their  eggs  in  the  ground.  In  northern  Africa  the  animals  be- 
come fat  in  the  autumn  and  hibernate  in  the  ground  during  the 
winter. 

.  The  common  chameleon  of  North  Africa,  Syria,  and  Asia 
Minor  is  ChamcBleon  vulgaris  (Fig.  452).  It  is  usually  greenish 
in  color  and  reaches  a  length  of  from  eight  inches  to  a  foot,  about 
half  of  which  consists  of  the  tail. 

Suborder  2.  Sauria.  —  Lizards.  —  The  lizards  constitute  a 
very  diversified  group  of  reptiles.  They  usually  have  an  elon- 
gated body  and  four  well-developed  limbs  that  are  used  for  run- 
ning, clinging,  climbing,  or  digging.  Some  have  no  limbs  or  only 
vestiges,  but  the  pectoral  and  pelvic  girdles  are  always  present 
and  there  is  usually  a  trace  of  a  sternum.  The  tail  is  generally 
long;  it  is  easily  broken  off,  but  a  new  organ  is  soon  regenerated, 
which,  however,  does  not  possess  vertebrae.  The  eyelids  are 
movable  except  in  some  of  the  degenerate  burrowing  forms  in 
which  the  eyes  have  become  concealed  beneath  the  skin.  The 
skin  is  covered  with  small  scales. 

Lizards  are  in  most  cases  oviparous,  and  the  eggs  are  pro- 


552 


COLLEGE  ZOOLOGY 


tected  by  a  parchment-like  shell.  They  feed  largely  on  insects, 
worms,  and  other  small  animals,  but  many  are  exclusively 
vegetarian.  The  more  than  fifteen  hundred  and  twenty- five 
species  of  lizards  are  placed  in  two  hundred  and  fifty-seven 
genera  and  twenty  families.  Only  eight  of  these  families  are 
reviewed  in  the  following  paragraphs. 

Family  Geckonid^.  —  Geckos  (Fig.  453).  — This  is  a  large 
family  containing  forty-nine  genera  and  about  two  hundred  and 
seventy  species.     Geckos  inhabit  all  the  warmer  parts  of  the 

globe,  are  harm- 
less, and  usually 
nocturnal.  Many 
of  them  have  la- 
mellae under  the 
toes  (Fig.  453), 
which  enable  them 
to  climb  over  trees, 
rocks,  walls,  and 
ceilings.  Three 
species  occur  in 
North  America  — 
the  reef  geckos. 
Splicer  odactylus  no- 
tatus,  of  Florida, 
Cuba,  and  the 
Bahamas,  the  tubercular  gecko,  Phyllodactylus  tuberculosus,  of 
Lower  Cahfornia,  and  the  cape  gecko,  P.  unctus,  also  of  Lower 
California. 

The  genus  Sphcerodactylus  contains,  besides  reef  geckos, 
seventeen  species  inhabiting  Central  and  South  America  and 
the  West  Indies.  The  reef  gecko  is  about  three  inches  long. 
It  has  been  reported  from  Key  West,  Florida.  Phyllodactylus 
is  another  large  genus;  its  twenty- five  species  occur  in  tropical 
South  America,  Africa,  Australia,  and  islands  in  the  Medi- 
terranean. 


Fig.  453.  —  Geckos,  Hemidactylus  turicus  (left); 
Tareniola  mauritanica  (right).     (From  Gadow.) 


CLASS  REPTILIA 


553 


n^Sfi^^^wm- 


FiG.  454.  —  The  flying  dragon,  Draco  volans. 
(From  Gadow.) 


Family  AgamidtE.  —  Old  World  Lizards.  —  These  lizards 
can  be  readily  distinguished  by  the  position  of  their  teeth,  which 
are  set  on  the 
edges  of  the  jaw- 
bones (acrodont 
dentition)  and  not 
in  grooves  or 
sockets.  There 
are  thirty  genera 
and  about  two 
hundred  species 
in  the  family. 

The  flying- 
dragon,  Draco 
volans  (Fig.  454), 
is  a  species  whose 
sides  are  ex- 
panded  into  thin  membranes  supported  by  ribs.  These  mem- 
branes are  employed  as  a  parachute  when  leaping  from  tree 
to  tree,  and  are  folded  when  not  in  use.     It  is  about  ten  inches 

long  and  inhabits 
the  Malay  Penin- 
sula, Sumatra, 
Java,  and  Borneo. 
Members  of  the 
genus  Calotes  have 
the  power  of  chang- 
ing  their  colors 
rapidly.  Another 
interesting  genus  is 
Chlamydosaurus, 
which  includes  the 
frilled  lizard,  C 
kingi  (Fig.  455). 
This     species     in- 


FiG.  455-  —  The  frilled  lizard,  Chlamydosaurus 
•kingi,  at  bay.     (From  Gadow.) 


554 


COLLEGE  200L0GY 


habits  Queensland  and  northern  Austraha  and  reaches  a  length 
of  about  three  feet.  The  skin  at  the  sides  of  the  neck  is  ex- 
panded into  a  sort  of  frill,  and  when  the  animal  is  irritated, 
this  frill  is  extended  by  means  of  rib-like  horns  of  the  hyoid 
apparatus. 

Family  Iguanid^e.  —  New  World  Lizards.  —  All  but  three 
of  the  forty-eight  genera  belonging  to  this  family  are  confined 
to  America.  The  habits  of  these  lizards  vary  considerably. 
Some  are  arboreal;  others  terrestrial;  and  still  others  semi- 
aquatic.    The  anoles,   often  called   chameleons,  the  iguanas, 

the  swifts,  and  the 
horned  "  toads  " 
are  the  best- 
known  groups. 

The  genus 
Anolis  contains 
over  one  hundred 
species.  These 
are  mostly  small,^ 
with  a  long, 
slender  tail.  They 
have  the  power  of 
changing  color 
rapidly  and  are 
popularly  called 
''  chameleons."  They  are  enabled  to  run  about  on  smooth, 
vertical  surfaces  by  lamellae  under  the  central  portion  of  each 
toe.  Anolis  carolinensis,  the  American  "  chameleon,"  is 
common  in  the  southeastern  United  States  and  in  Cuba. 

The  iguanas  range  from  the  southwestern  United  States  south- 
ward through  tropical  South  America.  The  marine  iguana, 
Amblyrhynchus  cristatus,  lives  on  the  Galapagos  Islands. 
Colonies  of  these  iguanas,  many  of  the  individuals  being  over 
four  feet  long,  inhabit  the  sea-coast  and  feed  on  seaweed.  The 
common  iguana.  Iguana  tuberculata  (Fig.  456),  reaches  a  length 


Fig.  456.  —  The  commo;i  iguana,  Iguana  tuberculata. 
(From  Gadow.) 


CLASS  REPTILIA 


555 


of  six  feet.  It  inhabits  tropical  America  and  is  a  favorite  article 
of  food.  It  loves  to  bask  in  the  sun,  lying  stretched  out  on  a 
stone  fence  or  the  limbs  of  a  tree.  The  food  of  this  iguana  con- 
sists largely  of  insects,  but  it  will  also  take  small  animals,  and 
certain  kinds  of  vegetation.  ", 

The  swifts  belong  to  the  genera  JJta  and  Sceloporus.  They 
are  common  in  western  North  America,  Mexico,  and  Central 
America.  Most  of  them  are  small,  and,  as  their  popular  name 
implies,  very  active.     The  sixteen  species  of  small-scaled  swifts 


Fig.  457.  — The  horned  "  toad,"  Phrynosoma  coronaium.     (From  Gadow.) 


are  included  in  the  genus  Uta.  They  live  in  the  arid  regions 
of  the  Southwestern  states  and  are  all  terrestrial.  The  genus 
Sceloporus  contains  about  thirty- five  species  of  spiny  swifts. 
The  scales  on  the  dorsal  surface  of  the  body  terminate  in  sharp, 
spine-like  points. 

The  horned  ''  toads  "  (genus  Phrynosoma,  Fig.  457)  occur  in 
the  western  United  States  and  in  Mexico.  They  live  in  hot,  dry 
regions,  many  of  them  inhabiting  the  deserts,  where  they  run 
about  in  search  of  insects  for  food.  They  are  viviparous. 
Horned  "  toads  "  can  be  kept  very  easily  in  captivity  if  placed 
in  a  warm,  dry  place  and  fed  on  meal  worms. 

Family  Anguid^.  —  Old  and  New  World  Lizards.  —  These 
lizards  have  a  deep  fold  on  each  side  of  the  body.     Most  of  them 


556 


COLLEGE  ZOOLOGY 


Fig.  458. — A  limbless  lizard,  Anguis  fragilis,  the 
"  slow-worm"  or  "  blind-worm."  (From  Shipley  and 
MacBride.) 


tail. 


have  poorly  developed  limbs  or  none  at  all.     The  glass  "  snakes,'* 
Ophisaurus  apus  of  Europe,  and  O.  ventralis  of  America,  have 

no  limbs  and  move, 
as  do  snakes,  by- 
lateral  undula- 
tions. They  can  be 
distinguished  from 
true  snakes  by  the 
presence  of  mov- 
able eyelids  and 
an  ear  opening. 
Their  name  is  due 
to  the  extreme 
brittleness  of  the 
Another  species,  called  the  "  blind-worm "  or  "  slow- 
worm,"  Anguis  fragilis  (Fig.  458),  inhabits  Europe,  western 
Asia,  and  Algeria.  It  looks  like  a  large,  brightly  colored 
worm,  but  is  not  blind,  since  it  has  well-developed  eyes. 

Family  Helo- 
dermatid^.  — 
Beaded  Lizards. 
— The  two  species 
included  in  this 
family  are  the  gila 
monster,  Helo- 
derma  sus pedum, 
of  Arizona  and 
New  Mexico,  and 
the  beaded  lizard^ 
H.  horridum,  of 
Mexico  and  Cen- 
tral America. 
The  gila  monster 

(Fig.  459)  is  the  only  poisonous  lizard  of  the  United  States. 
It  has  a  stout  body  and  is  conspicuously  colored  with  bright 


Fig.  459. 


The  Gila  monster,  Heloderma  suspectum. 
(From  Gadow.) 


CLASS   REPTILIA  557 

red  and  black.  A  large  specimen  measures  a  foot  and  one  half 
in  length.  Gila  monsters  possess  grooved  fangs  on  the  lower 
jaw,  and,  when  fighting,  viciously  grasp  their  prey  and  throw 
themselves  on  their  back,  thus  allowing  the  poison  to  flow  down 
into  the  wound.  The  bite  is  fatal  to  small  animals  and  dan- 
gerous to  man.  ' 

Family  Amphisb^nid^.  —  Worm  Lizards.  —  These  are 
limbless,  burrowing  lizards  resembling  worms  in  appearance. 
There  are  about  ten  genera  and  sixty  species  known  from  both 
the  Old  and  New  Worlds.  Of  these  only  one,  the  Florida  worm 
lizard,  Rhineura  floridana,  is  found  in  the  United  States.  This 
species  is  restricted  to  the  Florida  peninsula.  It  is  about  eight 
inches  long. 

Family  Lacertid^.  —  Typical  Old-world  Lizards.  — 
There  are  seventeen  genera  and  about  ninety-six  species  of 
lizards  that  are  included  in  this  family.  They  all  possess  well- 
developed  limbs,  and  a  long,  fragile  tail.  The  green  Uzard, 
Lacerta  viridis,  is  a  species  common  in  central  and  southern 
Europe.     Lacerta  vivipara  of  Europe  is  viviparous. 

Family  Scincid^e.  —  Skinks. — The  skinks  are  found  in 
many  parts  of  the  globe.  In  North  America  there  are  two 
genera  and  fifteen  species.  Eumeces  quinguelineatus,  the  five- 
lined  or  blue  skink,  is  the  species  common  in  the  Eastern 
and  Central  states.  The  young  are  black  with  a  longitudinal 
yellow  stripe  on  the  back  and  two  on  either  side,  and  a  blue  tail. 
The  females  "  retain  dull  stripes  through  life,  but  the  males 
become^  uniform,  dull  oHve-brown  on  the  body  and  bright  red 
about  the  head."  This  color  change  has  been  the  cause  of  several 
specific  and  common  names.  The  length  of  this  skink  is  about 
nine  inches. 

Suborder  3.  Serpentes.  —  Snakes. — The  snakes  resemble 
the  lizards  and  chameleons  in  many  of  their  anatomical  features. 
They  differ  from  them  in  at  least  four  respects:  (i)  the  right 
and  left  halves  of  the  lower  jaw  are  not  firmly  united,  but  are 
connected  by  an  elastic  band;    (2)  there  is  no  pectoral  girdle; 


558  COLLEGE  ZOOLOGY 

(3)  the  urinary  bladder  is  absent;  and  (4)  the  brain  case  is 
closed  anteriorly. 

Snakes  are  covered  with  scales;  those  on  the  head  are  so 
regular  as  to  be  of  importance  in  classification.  On  the  ventral 
surface  in  front  of  the  anus  is  a  single  row  of  broad  scales,  called 
abdominal  scutes,  to  which  the  ends  of  the  ribs  are  attached. 
The  outer,  horny  layer  of  the  skin  is  shed  a  number  of  times 
during  the  year.  Appendages  are  entirely  absent  except 
in  a  few  species,  like  the  python,  which  possess  a  pair  of 
short  spur-like  projections  one  on  either  side  of  the  anus,  — 
vestiges  of  the  hind  limbs.  The  eyelids  are  fused  over  the 
eyes,  but  there  is  a  transparent  portion  which  allows  the 
animal  to  see.  When  the  skin  is  being  shed,  the  snake  is 
partially  blind. 

There  is  no.  tympanic  membrane,  and  the  sense  of  hearing 
is  very  slightly  developed.  The  tongue  is  a  slender,  deeply 
notched  protrusible  structure  that  can  be  thrust  out  even  when 
the  mouth  is  closed,  because  of  the  presence  of  grooves  in  the 
jaws.  It  is  very  sensitive  to  vibrations  and  probably  serves  as  an 
organ  of  hearing.  The  prevalent  idea  that  the  tongue  can  inflict 
an  injury  is  erroneous.  The  teeth  are  sharp  and  recurved. 
They  are  adapted  for  forcing  the  food  into  the  throat.  In  the 
venomous  snakes  certain  teeth  are  grooved  or  tubular,  and  serve 
to  conduct  poison  into  any  object  bitten. 

The  bones  of  the  skull  are  so  arranged  that  the  jaws  are  ex- 
tremely mobile.  The  snake  is  on  this  account  able  to  swallow 
objects  four  or  five  times  the  diameter  of  its  neck.  When 
swallowing,  the  glottis  is  pulled  forward,  thus  preventing  the 
snake  from  choking.  The  vertebrae  are  very  numerous  — 
there  may  be  over  four  hundred  —  and  a  large  number  of  ribs 
are  also  present. 

Movement  on  land  is  accompanied  by  lateral  undulations  of 
the  body.  The  body  is  drawn  forward  by  pressing  the  rough 
posterior  edges  of  the  abdominal  scutes  against  the  substratum. 
Snakes   cannot  move   forward   on   a   smooth   surface.     Most 


CLASS  REPTILIA  559 

species  are  able  to  swim,  and  this,  of  course,  is  the  normal  method 
of  locomotion  of  the  aquatic  forms. 

The  majority  of  snakes  are  oviparous,  but  some  of  them  bring 
forth  their  young  alive.  The  idea  that  they  swallow  their 
young  in  order  to  protect  them  and  then  spew  them  out  again 
when  the  danger  has  passed  is  erroneous. 

The  tropics  are  more  plentifully  supplied  with  snakes  than  are 
the  temperate  zones.  Snakes  are,  however,  found  in  many 
places  not  inhabited  by  lizards.  Madagascar  seems  to  be  the 
only  large  country  in  warm  and  temperate  latitude  not  inhabited 
by  dangerous  snakes.  As  in  the  other  groups  of  vertebrates, 
the  serpents  are  found  in  almost  every  kind  of  habitat;  some 
species  live  in  salt  water,  others  in  fresh  water;  some  are 
arboreal;  and  many  live  underground. 

Only  four  of  the  nine  families  of  Serpentes  occur  in  North 
America.  With  a  few  exceptions  those  described  below  are 
found  in  the  United  States. 

Family  Glauconiid.'E.  —  Blind  Snakes.  —  Two  species  of 
these  small,  burrowing  reptiles  occur  in  the  United  States  — 
Glaucoma  dulcis,  the  Texas  blind  snake,  in  Texas  and  New 
Mexico,  and  G.  humilis,  the  California  blind  snake,  in  Arizona, 
and  southern  California.  They  dig  long  tunnels  in  the  earth 
and  feed  on  w^orms  and  insect  larvae. 

Family  BoiDiE.  —  Pythons  and  Boas. — The  members  of  the 
family  Boid^  are  constrictors.  They  live  almost  exclusively 
upon  birds  and  mammals  which  they  squeeze  to  death  in  their 
coils  (Fig.  460).  None  of  .them  is  venomous  and  only  a  few  are 
large  enough  to  be  dangerous  to  man.  The  largest  species  on 
record  is  the  regal  python,  Python  reticulatus,  of  Burma,  which 
attains  a  length  of  thirty  feet.  The  anaconda  or  water  boa, 
Eunectes  murinus,  of  South  America  averages  about  seventeen 
feet  in  length. 

Not  all  of  the  Boid^e  are  large.  Many  of  them  are  of  moderate 
size  or  even  small.  Four  species  are  found  in  North  America, 
but  they  are  comparatively  rare  and  confined  to  the  South- 


56o 


COLLEGE  ZOOLOGY 


Fig.  460. 


-  The  python,  Python  molurus,  devouring 
a  mammal.     (From  Gadow.) 


western  states. 
There  is  only  one 
"  boa-constrictor  " 
with  several  varie- 
ties. It  belongs  to 
the  genus  Boa  and 
its  specific  name  is 
constrictor.  It  is  a 
native  of  tropical 
South  America  and 
reaches  a  length  of 
eleven  feet.  Boa- 
constrictors  are 
docile  in  captivity 

and  therefore  preferred  by  snake  "  charmers." 

Family  Colubrid^.  —  This   family   contains  about  90  per 

cent  of  all  living  snakes  and  is  so  large  that  it  is  usually  divided 

into  three  series. 

Series  A.  Aglypha.  —  The  snakes  placed  in  this  series  have 

solid  teeth,  and  no  grooved  nor  perforated  fangs.     They  are  all 

non-venomous  and  are  found  in  every  country  inhabited  by 

snakes.     Half    a 

dozen  of  the  most 

common    species 

found  in  the  United 

States    are    briefly 

described  below. 
The    common 

garter-snake    or 

striped     snake, 

Thamnophis  sirtalis 

(Fig.  46 1 ) ,  is  usually 

provided  with  three 

longitudinal  yellow      ^7^  ^^^^  _  r^^^  garter-snake,  Thamnophis  sirtalis, 
stripes,  one  on  the  (From  Gadow.) 


CLASS  REPtiLtA  561 

back  and  one  on  either  side.  Every  portion  of  North  America 
is  inhabited  by  a  species  or  variety  of  this  genus.  The  garter- 
snakes  are  so  difficult  to  classify  that  our  description  must  be 
only  a  general  one.  The  species  T.  sirtalis  possesses  nineteen 
rows  of  scales  on  the  body,  and-  certain  peculiarities  in  the 
scales  (shields)  on  the  chin.  The  garter-snakes  are  the  most 
abundant  of  our  harmless  snakes.  They  are  the  first  to  appear 
in  the  spring  and  the  last  to  hibernate  in  the  autumn.  Their 
food  consists  largely  of  frogs,  toads,  fishes,  and  earthworms. 
The  young  are  brought  forth  alive,  usually  in  August,  and 
become  mature  in  about  one  year. 

The  common  water-snake.  Matrix  fasciatus  variety  sipedoftj 
belongs  to  a  genus  whose  species  and  varieties  are  abundant  in 
the  United  States,  Europe,  and  Asia.  They  are  semiaquatic 
serpents,  living  in  swampy  places  or  in  the  vicinity  of  ponds  and 
streams.  The  water  is  usually  selected  by  them  as  an  avenue 
of  escape  when  disturbed.  The  variety  sipedon  of  the  eastern 
United  States  is  pale  brownish  or  reddish  in  color,  with  wavy 
cross  bands  of  brown ;  these  break  up  into  blotches  on  the  hinder 
part  of  the  body.  The  length  of  an  adult  is  usually  about  three 
feet  six  inches.  Like  the  garter-snake,  the  water-snake  is  vivip- 
arous and  about  twenty-five  young  are  produced  in  August 
or  September.  The  water-snake  is  often  erroneously  called 
"  water-moccasin." 

The  black-snake,  Zamenis  constrictor ,  is  a  slender,  long-tailed 
snake  of  the  eastern  United  States  which  reaches  a  length  of  six 
feet.  West  of  the  Mississippi  it  gives  way  to  a  color  variety 
Z.  constrictor  variety  flaviventris,  called  the  "  blue  "  racer. 
In  the  East  the  black-snake  is  slaty  black  except  the  chin  and 
throat,  which  are  milky  white.  In  Michigan  and  adjoining  states 
it  is  bluish  green  above  and  immaculate  white  beneath.  Con- 
trary to  popular  belief,  this  reptile  does  not  attack  snakes  larger 
than  itself,  has  no  power  to  squeeze  its  prey  to  death,  and  is 
unable  to  hypnotize  birds  and  squirrels.  Its  prey  is  almost 
always  smaller  than  itself,  and  is  swallowed  while  still  alive,  often 
2  o 


562  COLLEGE   ZOOLOGY 

being  held  down  by  a  portion  of  the  body  during  the  process. 
Black-snakes  prefer  dry  and  open  situations,  especially  at  the 
edge  of  meadows.  They  are  partial  to  birds'  eggs  and  young, 
but  also  devour  mice,  frogs,  and  various  other  small  animals. 
Their  eggs  to  the  number  of  a  dozen  or  more  are  deposited  in 
June  or  July,  usually  under  a  stone  or  in  soft,  moist  soil. 

The  king-snakes  belong  to  the  genus  Ophibolus.  They  are  of 
various  sizes,  are  constrictors,  and  have  received  their  common 
name  because  they  prey  on  other  snakes.  Of  the  seven  species 
occurring  in  the  United  States,  the  milk-snake,  O.  doliatus  variety 
triangulus,  the  scarlet  king-snake  or  "  coral-snake,"  O.  doliatus 
variety  coccineuSy  and  the  common  king-snake,  O.  getulus,  are  of 
special  interest. 

The  milk-snake  derives  its  name  from  its  supposed  habit  of 
stealing  milk  from  cows.  This  is  not  true,  since  rats  and  mice 
are  its  principal  articles  of  food.  The  color  of  this  variety  is 
gray  above,  with  brownish  saddle-shaped  blotches  on  the  back, 
and  smaller  blotches  on  the  sides.  It  averages  about  three  feet  in 
length,  and  is  oviparous. 

The  scarlet  king-snake  or  "  coral-snake  "  is  a  small  variety 
about  a  foot  long.  It  is  ringed  with  bright  bands  of  scarlet, 
yellow,  and  black,  causing  it  to  resemble  the  venomous  coral- 
snake,  Elaps  fulvius  (see  p.  564). 

The  common  king-snake  or  chain-snake  is  a  heavy-bodied 
constrictor  of  the  eastern  United  States.  Other  snakes,  both 
harmless  and  venomous  species,  and  field  mice,  are  squeezed  to 
death  and  devoured  by  it.  King-snakes  are  immune  to  venom 
and  do  not  hesitate  to  attack  rattlesnakes,  water-moccasins, 
and  copperheads.  The  length  of  an  average  adult  is  about  five 
feet. 

The  hog-nosed  snakes  of  the  genus  Heterodon  are  represented 
in  North  America  by  three  species  popularly  known  as  "  puff- 
adders,"  "  spreading  vipers,"  or  "  blow  snakes."  The  common 
hog-nosed  snake,  Heterodon  platrhinus,  inhabits  dry,  sandy 
places  over  most  of  the  United  States  east  of  the  Rocky  Moun- 


CLASS  REPTILIA  563 

tains.  The  snout  is  turned  up  at  the  end,  whence  its  common 
name.  It  is  non-venomous  and  entirely  harmless,  but  when 
disturbed  throws  itself  into  a  defiant  attitude,  dilates  its  neck  Uke 
a  cobra,  and  makes  a  hissing  sound.  If  this  does  not  frighten 
away  the  enemy,  the  snake  may  syddenly  open  its  mouth,  and 
appear  to  be  injured  and  to  lose  strength.  ''  Then  a  convulsion 
seemingly  seizes  the  snake,  as  it  contorts  its  body  into  irregular 
undulations,  ending  in  a  spasmodic  wriggling  of  the  tail,  when 
the  reptile  turns  on  its  back  and  lies  Hmp  and  to  all  appearances 
dead. 

"  So  cleverly  and  patiently  does  the  snake  feign  death  that 
it  may  be  carried  about  by  the  tail  for  half  an  hour  or  more, 
hung  over  a  fence  rail  where  it  dangles  and  sways  to  a  passing 
breeze,  or  tied  in  a  knot  and  thrown  in  the  road,  and  to  all  of 
this  treatment  there  is  no  sign  of  life  except  from  one  condition. 
In  spite  of  this  remarkable  shamming,  the  snake  may  be  led  to 
betray  itself  if  placed  upon  the  ground  on  its  crawling  surface. 
Then  like  a  flash  it  turns  upon  its  back  again  and  once  more  be- 
comes limp  and  apparently  lifeless.  It  appears,  according  to  this 
creature's  reasoning,  that  a  snake  to  look  thoroughly  dead  should 
be  lying  upon  its  back.  This  idea  is  persistent,  and  the  experi- 
ment may  be  repeated  a  dozen  times  or  more. 

"  Should  the  observer  retreat  some  distance  away,  while  the 
reptile  Hes  thus,  or  he  seek  near-by  concealment,  the  craftiness 
of  the  animal  may  be  realized.  Seeing  nothing  further  to  alarm, 
the  serpent  raises  its  head  slightly  and  surveys  its  surroundings, 
and  if  there  is  no  further  sign  of  the  enemy,  it  quickly  rolls  over 
upon  its  abdomen  and  glides  away  as  fast  as  its  thick  body  will 
carry  it.  But  at  such  a  moment  a  move  on  the  observer's  part 
would  send  the  reptile  on  its  back  again,  with  ludicrous  pre- 
cipitation."    (Ditmars.) 

Series  B.  Opisthoglypha. — The  opisthoglyphs  are  Colu- 
BRiDiE  which  possess  grooved  teeth  in  the  rear  of  the  upper  jaw. 
They  are  all  poisonous,  but  very  few  are  dangerous  to  man. 
The    subfamily   Homalopsin^e   contains    about    twenty-three 


564  COLLEGE  ZOOLOGY 

species  of  fish-eating,  river  snakes  of  the  East  Indies.  The  sub- 
family DiPSADOMORPHiN^  Contains  about  two  hundred  and 
seventy- five  species  of  slender,  long-tailed  snakes  of  cosmopolitan 
distribution.  They  are  terrestrial,  sub  terrestrial,  arboreal, 
or  semiaquatic  in  habits.  The  opisthoglyphs  of  the  United 
States  are  found  only  in  the  southern  part.  They  are  moderate 
or  small  in  size,  few  in  number,  and  not  very  dangerous. 

Series  C.  Proteroglypha.  —  The  proteroglyphs  are  CoLU- 
BRiD^  which  possess  fixed,  tubular  fangs  in  the  anterior  part 
of  the  upper  jaw.  As  in  the  case  of  the  opisthoglypha,  they  are 
all  venomous.  Many  of  them  are  the  most  dangerous  of  all 
poisonous  reptiles.    There  are  two  subfamilies. 

The  Hydrin^,  or  sea-snakes,  are  true  sea-serpents.  They 
inhabit  the  Indian  Ocean  and  the  w^estern,  tropical  Pacific, 
and  one  species  occurs  along  the  western  coast  of  tropical 
America.  They  reach  a  length  of  from  three  to  eight  feet  or 
more,  and  most  of  them  are  very  poisonous.  The  tail,  and  some- 
times the  body,  is  laterally  compressed  —  an  adaptation  for 
swimming. 

The  subfamily  Elapin^e  contains  twenty-nine  genera  and 
about  one  hundred  and  fifty  species  of  poisonous  snakes.  They 
are  most  abundant  in  AustraUa  and  New  Guinea,  but  occur  also 
in  India,  Malaysia,  Africa,  and  America.  The  single  genus 
Elaps  of  the  New  World  contains  about  twenty-eight  species 
of  coral-snakes.  Two  of  these  are  found  in  the  United  States, 
the  harlequin  or  coral  snake,  Elap^  fulvius,  and  the  Sonoran 
coral-snake,  E.  euryxanthus. 

The  harlequin  snake  of  the  southeastern  United  States  aver- 
ages about  two  and  a  half  feet  in  length.  Its  body  is  ringed  by 
broad  cross  bands  of  scarlet  and  blue-black,  separated  by  nar- 
row bands  of  yellow.  It  can  easily  be  distinguished  from  the 
harmless  scarlet  king-snake  (p.  562),  since  in  the  latter  the  yellow 
bands  are  bordered  by  the  black  ones.  The  harlequin  snake 
burrows  in  the  ground,  and  feeds  chiefly  upon  lizards  and  snakes. 
It  is  oviparous.     Most  writers  consider  this  snake  dangerous 


CLASS  REPTILIA 


565 


only  to  small  animals,  but  its  fangs  are  capable  of  injecting  a 
venom  more  virulent  than  that  of  the  rattlesnake. 

The  cobra-de-capello,  Naja  tripudians  (Fig.  462),  of  India, 
China,  and  the  Malay  Archipelago,  is  the  most  notorious  relative 
of  the  harlequin  snake.  The  cobra  is  very  vicious;  when  dis- 
turbed it  raises  the  anterior  part  of  the  body  from  the  ground, 
spreads  its  neck  (hood)  with  a  hiss,  and  strikes  at  once.  In 
India  the  bare-legged  natives  are 
killed  in  large  numbers  by  cobras; 
for  example,  in  1908,  21,880  were 
killed  by  snake  bites,  most  of  them 
probably  the  bites  of  this  species. 
There  are  nine  other  species  of 
cobras  —  seven  confined  to  Africa, 
one  in  the  Philippine  Islands,  and 
one,  the  king  cobra,  inhabiting  the 
same  countries  as  the  cobra-de- 
capello. 

Family  Viperid^. — Thick- 
bodied  Poisonous  Snakes.  —  The 
viperine  snakes  are  often  termed 
solenoglyphs  to  distinguish  them 
from  the  three  series  of  the  family  Colubrid^e.  Their  fangs 
are  tubular,  firmly  attached  to  the  movable  maxillary  bones, 
and  folded  flat  against  the  roof  of  the  mouth  when  the  jaws 
are  closed.  The  two  subfamilies  of  viperine  snakes  are  the 
ViPERiNyE,  or  true  vipers,  of  the  Old  World,  and  the  Crotalin^, 
or  pit-vipers,  of  both  the  New  World  and  Old  World. 

The  pit- vipers  are  easily  recognized  by  the  presence  of  a  deep 
pit  on  each  side  of  the  head  between  the  eye  and  the  nostril. 
The  function  of  this  pit  is  not  known.  There  are  four  genera 
and  about  seventy  species.  Those  found  in  the  United  States 
are  the  copperhead,  water-moccasin,  and  fifteen  species  of 
rattlesnakes. 

The  water-moccasin,  Agkistrodon  piscivorus  (Fig.  463),  occurs 


Fig.  462.  —  The  cobra,  Naja 
tripudians.  _  (From  Gadow.) 


566 


COLLEGE  ZOOLOGY 


Fig.  463.  —  The  water-tnoccasin,  Agkislrodon 
piscivorus.     (From  Gadow.) 


in  the  swamps  of  the  Atlantic  coast  south  of  North   Caro- 
lina,   and     in    the     Mississippi    Valley    from    southern     Illi- 
nois and  Indiana 
southward.      The 
length  of  an  aver- 
•  age    specimen    is 
four   feet,   but   a 
length  of  over  five 
feet  is  sometimes 
attained.       The 
moccasin  is  one  of 
the  most  poison- 
ous of  all  snakes. 
It    feeds   upon 
cold-blooded  ani- 
mals such  as  frogs, 
and     also     upon 
small  birds  and  mammals.     The  young  are  brought  forth  alive. 
The  copperhead  snake,  Agkislrodon  contortrix  (Fig.  464),  is 

another  very  yen- __^— _  ^ 

omous  snake.  Its 
range  extends  from 
southern  Massa- 
chusetts to  north- 
ern Florida  and 
west  to  Texas.  In 
the  southern  part 
of  its  range  the 
copperhead  prefers 
to  live  on  the 
plantations,  but  in 
the  North  it  is 
found   in  or  near 

thick  forests.     An  average  specimen  measures  about  two  and 
a  half  feet  in  length. 


Fig.  464.  —  The  copperhead,  Agkislrodon  contortrix. 
(From  Gadow.) 


CLASS   REPTILIA 


567 


The  rattlesnakes  are  easily  distinguished  by  the  rattle  at  the 
end  of  the  tail.  This  consists  of  a  number  of  horny,  bell-shaped 
segments  loosely  held  together.  Each  segment  was  once  the 
end  of  the  tail;  it  was  shed  when  the  skin  was  shed,  but  was  held 
by  the  newly  developed  end  of  the  tail.  Rattles  are  therefore 
added  as  often  as  the  skin  is  shed,  and,  since  this  happens  several 
times  per  year,  and  also  since  rattles 
are  often  detached  and  lost,  it  is 
obvious  that  the  number  of  rattles  is 
no  indication  of  the  age  of  the  snake. 
Usually   before    striking,    the   rattle- 


Fig.  465.  —  Poison  apparatus  of  the  rattlesnake.  A,  A,  eye;  Gc,  poison- 
duct  entering  poison-fang  at  f ;  Km,  muscles  of  mastication,  cut  at  * ; 
Mc,  Mc',  constrictor  muscle;  N,  nasal  opening;  S,  fibrous  poison-sac; 
z,  tongue;  za,  opening  of  poison-duct;  zf,  pouch  of  mucous  membrane 
enclosing  poison-fangs.  B,  position  of  apparatus  when  mouth  is  closed. 
C,  position  when  mouth  is  opened  widely.  Di,  digastric  muscle:  G,  groove 
or  pit  characteristic  of  Crotaline  snakes;  J,  poison-fang;  M,  maxillary; 
P,  palatine;  Pe,  sphenopterygoid  muscle;  Pm,  premaxillary;  Pt,  pterygoid; 
Q,  quadrate;  Sq,  squamosal;  Ta,  insertion  of  anterior  temporal  muscle; 
Tr,  ectopterygoid.  (A,  from  Parker  and  Haswell,  after  Wiedersheim; 
B,   C,  from  Gadow.) 


snake  vibrates  the  end  of  the  .tail   rapidly,  producing  a  sort 
of  buzzing  noise,  which,  to  the  wise,  serves  as  a  warning. 

The  poison  apparatus  of  the  rattlesnake  is  shown  in  Figure 
465.  The  poison  is  secreted  by  a  pair  of  glands  (Fig.  465,  A,  S) 
lying  above  the  roof  of  the  mouth.  These  glands  open  by  poison 
ducts  (Gc)  into  the  poison-fangs  (f).  The  poison-fangs  are 
pierced  by  a  canal,  which  opens  near  the  end  (za),  and  are  en- 
closed by  a  pouch  of  mucous  membrane  (zf).     When  the  jaws 


568 


COLLEGE  ZOOLOGY 


are  closed  (Fig.  465,  B),  the  fangs  lie  back  against  the  roof  of 
the  mouth.  When  the  snake  bites,  the  digastric  muscle  (Fig. 
465,  C,  Di)  opens  the  jaws;  the  sphenopterygoid  muscle  (Pe) 
contracts,  pulls  the  pterygoid  bone  (Pt)  forward  and  pushes 
the  ectopterygoid  bone  {Tr)  against  the  maxillary  bone  (M). 
The  maxillary  bone  is  thus  rotated,  and  the  poison-fang  (/)  is 
erected.     The  poison-glands  are  so  situated  that  the  opening 

of  the  jaws  and  erection  of  the 
fangs  squeezes  the  poison  out 
of  them,  through  the  fangs, 
and  into  the  object  bitten. 
There  are  several  pairs  of 
small  fangs  lying  just  behind 
the  functional  ones,  which  are 
held  in  reserve  to  replace  those 
that  are  lost  in  struggles  with 
prey  or  are  normally  shed. 

Rattlesnakes  are  most  abun- 
dant both  as  regards  the  num- 
ber of  species  and  the  number 
of  individuals  in  the  deserts 
of  the  southwestern  United 
States,  but  almost  every  part 
of  this  country  is  inhabited 
by  one  or  more  species.  The 
diamond-back  rattlesnake,  Cro- 
talus  adamanteus,  is  the  most  deadly  and  largest  rattlesnake^ 
measuring  sometimes  over  eight  feet  in  length.  It  inhabits 
the  pine  swamps  and  hummock  lands  of  the  southeastern  United 
States.  A  nearly  allied  species  is  the  Texas  rattlesnake,  Crotalus 
atrox  (Fig.  466).  This  species  inhabits  the  subarid  and  desert 
regions  of  Texas  and  the  Southwest.  These  snakes  are  nocturnal 
in  habit,  and  prefer  the  common  rabbit  as  food.  Their  bite  is 
usually  fatal  to  man  within  an  hour. 

Other  species  that  should  be  mentioned  are  the  timber,  or 


Fig.  466. — The  Texas  rattlesnake, 
Crotalus  atrox.  (From  Shipley  and 
MacBride,  after  Baird  and  Girard.) 


CLASS   REPTILIA  569 

banded  rattlesnake,  Crotalus  horridus,  of  the  eastern  United 
States;  the  horned  rattlesnake,  Crotalus  cerastes,  inhabiting  the 
deserts  of  the  southwestern  United  States;  and  the  massasauga, 
Sistrurus  catenatus,  which  is  a  rather  common  species  in  the 
central  United  States. 

4.  The  Poisonous  Snakes  of  North  America 

As  the  preceding  discussion  shows,  there  are  only  twenty-two 
species  of  poisonous  snakes  in  the  United  States;  namely,  the 
harlequin  snake,  the  Sonoran  coral-snake,  the  copperhead,  the 
water-moccasin,  seven  unimportant  opisthoglyphs  (p.  563),  and 
fifteen  species  of  rattlesnakes.  It  is  important  for  any  one  who 
spends  much  time  in  the  country  to  be  able  to  distinguish  be- 
tween these  poisonous  snakes  and  the  non-poisonous  species. 
This  can  easily  be  done  by  means  of  the  following  key,  which  was 
prepared  by  Professor  Alexander  G.  Ruthven. 

Key  to  the   Venomous  and  Non-venomous  Snakes  of  the  United 

States 
A.   Pupil  of  eye  vertical. 

B.   A  pit  between  the  eye  and  nostril.  —  Pit- vipers  (venomous) 
C.    Tail  terminating  in  a  rattle  .  .  .  Rattlesnakes. 
CC.   Tail  not   terminating   in   a   rattle.  —  Moccasin   and 
copperhead. 
BB.   No  pit  between  eye  and  nostril.  —  Non-venomous  or 
opisthoglyph  and  not  dangerous  to  man. 
AA.   Pupil  of  eye  round. 

B.  Body  ringed  with  red,  black,  and  yellow,  the  black  rings 
bordered  by  the  yellow  ones.  —  Coral-snakes  (venom- 
ous). 
BB.  Body  not  ringed  with  red,  black,  and  yellow,  or  if  so  the 
yellow  rings  bordered  by  the  black  ones.  —  Non- 
venomous  or  opisthoglyph  and  not  dangerous  to 
man. 


570 


COLLEGE  ZOOLOGY 


Notwithstanding  the  fear  of  snakes  possessed  by  most  people, 
very  few  are  bitten  by  poisonous  species  in  this  country,  and  of 
these  probably  not  more  than  two  per  year  die. 

Snake  Venom.  —  Venom  is  a  highly  complex  physiological 
product  elaborated  by  the  poison-glands.  Among  its  powers  are 
the  dissolution  of  various  body  cells  and  the  destruction  of  the 
bactericidal  property  of  the  blood.  Venoms  are  albuminoid. 
They  are  capable  of  producing  in  the  blood  an  antidote  or 
neutralizing  substance,  called  an  antibody.  It  is  thus  possible, 
as  in  the  case  of  smallpox,  tetanus,  etc.,  to  obtain  an  antibody 
(an  antivenin)  which,  when  injected  into  the  blood,  will  counter- 
act the  effects  of  the  venom.  Unfortunately  each  kind  of  venom 
requires  a  special  sort  of  antivenin,  so  that  it  is  impracticable 
as  a  rule  to  carry  antivenin  into  the  field. 

The  best  method  of  procedure  when  bitten  by  a  poisonous 
snake  is  to  apply  a  ligature  between  the  wound  and  the  heart  so 
as  to  prevent  the  blood  from  carrying  the  venom  toward  the 
heart.  This  ligature  should  not  be  kept  on  more  than  half  an 
hour,  since,  as  stated  above,  the  venom  destroys  the  bactericidal 
power  of  the  blood,  and  gangrene  will  set  in  rapidly  about  the 
wound  if  fresh  blood  is  not  supplied.  After  the  ligature  is  in 
place,  the  wound  should  be  incised  deeply  in  all  directions,  and 
a  solution  of  potassium  permanganate  injected  freely  into  the 
tissues  about  the  wound.  This  treatment  should  serve  to  destroy 
most  of  the  venom  before  it  travels  far  in  the  system.  Sucking 
the  poison  from  the  wound  is  a  common  practice,  but  there  is 
danger  of  poison  finding  its  way  into  the  blood  through  slight 
abrasions  of  the  lips  or  mouth,  and,  besides,  this  procedure  is  of  no 
value.  It  also  seems  certain  that  the  drinking  of  large  quantities 
of  alcohol  is  not  only  useless,  but  of  considerable  detriment. 

5.  The  Economic  Importance  of  Reptiles 

The  economic  importance  of  the  various  kinds  of  reptiles  has 
been  emphasized  during  the  discussion  of  the  orders  and  families. 
It  will  therefore  suflSice  here  to  give  a  brief  summary  of  the  subject. 


CLASS   REPTILIA  571 

The  food  of  reptiles  consists  of  both  animals  and  plants.  The 
animals  eaten  belong  to  practically  all  classes.  Many  of  the 
snakes  live  almost  entirely  upon  birds  and  mammals.  Frogs, 
fish,  and  other  reptiles  are  favorite  articles  of  food.  Most  of  the 
smaller  species  of  reptiles  feed  upon  worms  and  insects.  In 
general  it  may  be  stated  that  reptiles  do  very  little  damage  be- 
cause of  the  animals  and  plants  they  destroy  for  food,  but  are 
often  of  considerable  benefit,  since  they  kill  large  numbers  of 
obnoxious  insects  and  other  forms. 

The  turtles  and  tortoises  rank  first  as  food  for  man.  Espe- 
cially worthy  of  mention  are  the  green  turtle  (p.  543) ,  the  diamond- 
back  terrapin  (p.  542),  and  the  soft-shelled  turtle  (p.  545).  In 
some  parts  of  this  country  it  would  seem  possible  to  establish 
turtle  farms  that  would  utilize  land  useless  for  other  purposes, 
and  would  be  commercially  successful.  Certain  lizards,  such  as 
the  iguana  of  tropical  America,  form  a  valuable  addition  to  the 
food  supply  in  various  localities. 

The  skins  of  the  crocodilians  are  used  rather  extensively  for 
the  manufacture  of  articles  that  need  to  combine  beauty  of 
surface  with  durability.  The  alligators  in  this  country  have 
decreased  so  rapidly  because  of  the  value  of  their  hides  that 
they  will  be  of  no  great  economic  importance  unless  they  are 
consistently  protected  or  grown  on  farms.  Of  less  value  are 
the  skins  of  certain  snakes.  Tortoise-shell,  especially  that 
procured  from  the  horny  covering  of  the  carapace  of  the  hawk's- 
bill  turtle  (p.  544,  Fig.  447),  is  widely  used  for  the  manufacture 
of  combs  and  ornaments  of  various  kinds. 

As  previously  stated,  the  poisonous  snakes  of  the  United  States 
are  of  very  little  danger  to  man.  In  tropical  countries,  espe- 
cially India  (p.  565),  venomous  snakes  cause  a  larger  death-rate 
than  that  of  any  other  group  of  animals.  The  Gila  monster, 
which  is  one  of  the  few  poisonous  lizards,  and  the  only  one  in- 
habiting the  United  States,  very  seldom  attacks  man,  and  prob- 
►ably  never  inflicts  a  fatal  wound. 


572 


COLLEGE  ZOOLOGY 


6.   Prehistoric  Reptiles 

Sixteen  of  the  twenty  orders  of  reptiles  are  known  only  from 
their  fossil  remains  embedded  in  the  earth's  crust.  Three  of 
these  orders  will  serve  to  give  a  general  idea  of  the  nature  of  the 
extinct  reptiles. 


Fig.  467. — Fossil  reptiles.  A,  Brontosaurus  excelsus.  B,  Stcgosaurus 
ungulatus.  C,  Ceratosaurus  nasicornis.  (A,  B,  from  Sedgwick's  Zoology, 
after  Marsh;    C,  from  Zittel,  after  Marsh.) 


CLASS   REPTILIA 


573 


Order  Dinosauria.  —  The  Dinosauria  were  extremely  large 
reptiles  that  probably  lived  in  swamps  or  in  the  neighborhood 
of  water  during  Triassic,  Jurassic,*and  Cretaceous  times.  Re- 
mains have  been  found  in  America,  Europe,  Asia,  Africa,  and 
Australia,  and  footprints  have  been  discovered  in  the  sandstone 
of  the  Connecticut  Valley.  Some  species  measured  over  one 
hundred  feet  in  length.  Both  herbivorous  and  carnivorous  forms 
existed. 

Brontosaurus  (Fig.  467,  A)  was  about  sixty  feet  long;  was 
herbivorous;  and  had  four  limbs  about  equally  well  developed. 
Its  remains  have  been  found  in  Wyoming  and  Colorado.  Steg- 
osaurus  (Fig.  467,  B)  reached  a  length  of  about  twenty-eight 
feet  and  was  also  herbivorous.  It  possessed  huge  triangular 
plates  along  the  back.  Remains  have  been  discovered  in  Wyo- 
ming and  Colorado.  Ceratosaurus  (Fig.  467,  C)  was  a  carnivorous 
dinosaur  with  a  comparatively  large  head.  The  character  of  its 
skeleton  indicates  that  it  walked  about  on  its  hind  limbs  and 
rested  on  its  tail,  much  like  a  kangaroo.  Remains  have  been 
found  in  Colorado. 

Order  Ichthyosauria.  —  The  Ichthyosaurs  (Fig.  468)  were 
fish-eating,    aquatic    reptiles.     Their    bodies    were    admirably 


Fig.  468.  —  A  fossil  reptile,  Ichthyosaurus  communis.     Caudal  fin  not  shown. 
(From  Parker  and  Haswell,  after  Owen.) 

adapted  for  life  in  the  water,  and  they  have  been  called  the 
"  whales  "  of  the  Mesozoic  Era.  The  remains  of  Ichthyosaurs 
occur  in  North  America,  Europe,  Asia,  Africa,  and  Australia. 

Order  Pterosauria.  —  The  Pterosauria  were  reptiles  of  the 
Mesozoic  Era  which  had  the  fore  limbs  modified  for  flight.  They 
resemble  birds  in  certain  skeletal  characters,  but  differ  from 


574 


COLLEGE  ZOOLOGY 


them  in  others.     Rhamphorhynchus  (Fig.  469)  possessed  teeth 
and  a  long  taiL     Pteranodon  is  the  largest  form  known;   it  had 


Fig.  469.  —  Restoration  of  a  fossil,  flying  reptile,  Rhamphorhynchus  phyllurus. 
(From  Sedgwick's  Zoology,  after  Woodward.) 


a  skull  two  feet  long,  and  a  spread  of  wing  of  twenty  feet.    Teeth 
are  absent,  and  the  tail  is  short. 


CHAPTER   XX 


SUBPHYLUM    VERTEBRATA:   CLASS    VI.    AVES 


L 


The  class  Aves  contains  the  birds.  Birds  are  easily  dis- 
tinguished from  all  other  animals,  since  they  alone  possess 
feathers.  The  ten  thousand  or  more  species  of  birds  are  grouped 
into  two  subclasses:  (i)  ARCHiEORNiXHES,  which  contains  the 
fossil  form  Archceopteryx ;  and  (2)  Neornithes,  which  contains 
four  orders  of  extinct  forms  and  seventeen  orders  with  Uving 
representatives. 

I.  The  Pigeon 

The  common  pigeons  have  been  derived  from  the  blue  rock- 
pigeon,  Columba  livia  (Fig.  470),  which  ranges  from  Europe 
through  the  Medi- 
terranean coun- 
tries to  central 
Asia  and  China. 
Since  pigeons  are 
easily  obtained 
and  of  moderate 
size,  they  are 
usually  selected 
as  a  type  of  the 
class  AvES  for 
laboratory  study. 

External  Fea- 
tures. — The  body 
of   the   pigeon   is 

spindle-shaped,  and  therefore  adapted  for  movement  through 
the  air.     Three  regions  may  be  recognized,  —  head,  neck,  and 

575 


Fig. 


470.  —  The  blue  rock  pigeon,  Columba  livia. 
(From  Brehm.) 


576 


COLLEGE  ZOOLOGY 


trunk.  The  head  is  prolonged  in  front  into  a  pointed,  horny 
beak,  at  the  base  of  which  is  a  patch  of  naked,  swollen  skin, 
the  cere.     Between  the  beak  and  the  cere  are  the  two  oblique, 


01     RJ  BW    MJ    M4   Ml 


Fig.  471.  —  Anatomy  of  the  pigeon.  A,  nostril;  AD,  ad-digital  primary 
feather;  B,  external  auditory  meatus;  BW,  bastard  wing;  C,  oesophagus; 
CA,  right  carotid  artery;  D,  crop;  DA,  aorta;  E,  keel  of  sternum;  F,  right 
auricle;  G,  right  ventricle;  HV,  hepatic  vein;  Hi,  left  bile-duct;  H2,  right 
bile-duct;  /,  distal  end  of  stomach;  I  A,  right  innominate  artery;  IV,  posterior 
vena  cava;  J  A,  left  innominate  artery;  JV,  right  jugular  vein;  K,  gizzard; 
L,  liver;  M,  duodenum;  MD,  mid-digital  primary  feathers;  MP,  metacarpal 
primaries;  Mi,  preaxial  metacarpal;  M2,  middle  metacarpal;  M3,  postaxial 
metacarpal ;  N,  cloacal  aperture ;  Ni,  preaxial  digit ;  O,  bursa  Fabricii, 
Oi,  proximal  phalanx  of  middle  digit;  O2,  distal  phalanx  of  middle  digit; 
P,  pancreas;  PA,  right  pectoral  artery;  PD,  predigital  primary;  PV ,  portal 
vein;  Pi,  first  pancreatic  duct;  P2,  second  pancreatic  duct;  P3,  third  pancre- 
atic duct;  Q,  pygostyle;  R,  rectum;  RC,  radial  carpal  bone;  RX,  rectrices; 
Ri,  ulnar  digit;  S,  ureter;  SA,  right  subclavian  artery;  SV,  right  anterior 
vena  cava;  T,  rectal  diverticulum;  U,  kidney;  UC,  ulnar  carpal  bone;  V,  pelvis; 
W,  lung;  X,  humerus;     F,  radius;    Z,  ulna.     (From  Marshall  and  Hurst.) 


slit-like  nostrils  (Fig.  471,  ^).  On  either  side  is  an  eye  which 
is  provided  with  upper  and  lower  lids,  and  with  a  well-developed 
third  eyelid,  or  nictitating  membrane.     The  third  eyelid  can  be 


CLASS  AVES 


577 


raJx 


drawn  across  the  eyeball  from  the  inner  angle  outward.  Below 
and  behind  each  eye  is  an  external  auditory  aperture  (Fig.  471,  B) 
which  leads  to  the  tympanic  cavity. 

The  neck  is  long  and  flexible.  At  the  posterior  end  of  the 
trunk  is  a  projection  which  beara  the  tail  feathers.  The  two 
wings  can  be 
folded  close  to 
the  body  or  ex- 
tended as  organs 
of  flight.  The 
hind  limbs  are 
covered  with 
horny  epidermal 
scales,  and  their 
digits  are  each 
provided  with  a 
horny  claw. 

Feathers.  — 
Feathers  are 
peculiar  to  birds. 
They  arise,  as 
do  the  scales  of 
reptiles,  from 
dermal  papillae 
with  a  covering 
of  epidermis, 
and  become  en- 

^1  1  •         _•,       rachis;  sup.umb,  superior  umbilicus 

veloped  m  a  pit,  Hasweii.) 
the  feather  fol- 
licle. A  typical  feather  (Fig.  472,  ^)  consists  of  a  stiff  axial  rod, 
the  scapus  or  stem  ;  the  proximal  portion  is  hollow,  and  semi  trans- 
parent, and  is  called  the  quill  or  calamus  {cat) ;  the  distal  portion 
is  called  the  vane,  and  that  part  of  the  stem  passing  through  it 
is  the  shaft  or  rachis  {rch).  The  vane  is  composed  of  a  series  of 
parallel  harhs,  and  each  barb  bears  a  fringe  of  small  processes, 
2  p 


ini'.zcrrhh 


Fig.  472. —  Feathers  of  the  pigeon.  A,  proximal  por- 
tion of  a  contour  feather.  B,  filoplume.  C,  nestling 
down,     cal,  calamus;    inf.umb,  inferior  umbilicus;    rch, 

(From  Parker  and 


578 


COLLEGE  ZOOLOGY 


the  barbules,  along  either  side.  The  barbules  on  one  side  of  the 
barb  bear  hooklets  which  hold  together  the  adjacent  barbs.  The 
whole  structure  is  thus  a  pliable,  but  nevertheless  resistant,  organ 
wonderfully  adapted  for  use  in  flight. 

The  three  principal  kinds  of  feathers  are:  (i)  the  contour 
feathers  or  pennae  like  that  just  described;  these  possess  a  stiff 
shaft  and  firm  vanes,  and  since  they  appear  on  the  surface, 
determine  to  a  large  degree  the  contour  of  the  body.     (2)  The 

down  feathers  or  plumulae 
possess  a  soft  shaft  and  a 
vane  without  barbs;  they 
lie  beneath  the  contour 
feathers  and  form  a  cover- 
ing for  the  retention  of 
heat.  The  barbs  of  some 
down  feathers  arise 
directly  from  the  end  of 
the  quill,  and  no  shaft  is 
present  (Fig.  472,  C). 
(3)  The  filoplumes  (B)  pos- 
sess   a    slender,    hair-like 


cd.pt 


Fig.  473.  —  Feather  tracts  of  the  pigeon. 
A,  ventral;  B,  dorsal,  al.pt,  alar  pteryla  or 
wing  tract;  c.pt,  cephalic  pteryla  or  head- 
tract;  ci.pl,  caudal  pteryla  or  tail  tract; 
cr.pt,  crural  pteryla;  cr  apt,  cervical  apte- 
rium.  or  neck-space;  jm.pt,  femoral  pteryla; 
hu.pt,  humeral  pteryla;  lat.apt,  lateral 
apterium;  sp.pt,  spinal  pteryla;  v.apt,  ven- 
tral apterium;  v.pt,  ventral  pteryla.  (From 
Parker  and  Haswell,  after  Nitzsch.) 


shaft  and  very  few  or  no 
barbs. 

Only  certain  portions  of 
the  pigeon's  body  bear 
feathers  ;  these  feather 
tracts  are  termed  pterylce, 
and  the  featherless  spaces  are  known  as  apteria.  The  feather 
tracts  differ  in  different  species  of  birds;  those  of  the  pigeon 
are  shown  in  Figure  473. 

Birds  shed  their  old  feathers,  i.e.  molt,  usually  in  the  fall, 
and  acquire  a  complete  new  set  which  are  formed  within  the 
follicles  and  from  the  papillae  of  those  that  are  cast  off.  There 
may  be  a  partial  molt  in  the  spring,  when  the  bird  assumes  its 
breeding  plumage.     At  this  time  the  plumage  often  changes 


CLASS   AVES 


579 


color;  this  is  caused  probably  either  by  an  actual  chemical 
change  in  the  pigment,  or  by  the  breaking  off  of  the  tips  of  the 
feathers. 

The  Skeleton.  —  The  principal  differences  between  the  skele- 
ton of  a  pigeon  and  that  of  a  reptile  are  those  that  are  made 
necessary  by  the  methods  of  locomotion  of  the  former.  The 
hind  limbs  and  pelvic  girdle  are  modified  for  bipedal  locomotion; 
the  fore  limbs  and  pectoral  girdle  are  modified  iox  flight;  the 
skeleton  of  the  trunk  is  rigid;  the  sternum  has  a  distinct  crest 
for  the  attachment  of  the  large  muscles  that  move  the  wings ; 
short  projections,  called  uncinate  processes,  which  extend  back- 
ward from  some  of  the  ribs,  make  the  thoracic  framework  more 
firm;  and  the  bones  are  very  light,  many  of  them  containing  air- 
cavities.  The  skeleton  of  the  common  fowl  (Fig.  474)  is  larger 
and  more  easily  studied  than  that  of  the  pigeon,  and  is  similar 
to  the  latter  in  most  respects. 

The  skull  (Fig.  474,  7-7)  is  very  light,  and  most  of  the  bones 
in  it  are  so  fused  together  that  they  can  be  distinguished  only 
in  the  young  bird.  The  cranium  is  rounded;  the  orbits  are 
large  ;  the  facial  bones  extend  forward  into  a  beak ;  the 
quadrate  is  movable  and  connects  the  lower  jaw  with  the 
squamosal  of  the  cranium ;  there  is  but  a  single  occipital 
condyle  for  articulation  with  the  first  vertebra;  and  no  teeth 
are  present. 

The  cervical  vertebrae  (Fig.  474,  8)  are  long  and  move  freely 
upon  one  another  by  saddle-shaped  articular  surfaces,  making 
the  neck  very  flexible.  This  enables  the  bird  to  use  its  bill  for 
feeding,  for  nest  building,  and  for  many  other  purposes.  The 
vertebrae  of  the  trunk  are  almost  completely  fused  together  into 
a  rigid  skeletal  axis  which  is  necessary  to  support  the  body  while 
in  flight.  There  are  four  or  five  free  caudal  vertebrae  followed 
by  a  terminal  pygostyle  (Fig.  474,  18)  consisting  of  five  or  six 
fused  vertebrae.  The  pygostyle  (Fig.  471,  Q)  supports  the  large 
tail  feathers  (rectrices.  Fig.  471,  RX),  and  the  free  caudal  ver- 
tebrae allow  the  movements  of  the  tail  which  enable  the  bird  to 


58o 


COLLEGE  ZOOLOGY 


83 

12 


Fig.  474-  — Skeleton  of  the 
common  fowl,  male.  /,  pre- 
maxilla;  2,  nasal;  j,  lachry- 
mal; 4,  frontal;  5,  mandible; 

6,  lower    temporal    arcade; 

7,  tympanic  cavity;  8,  cer- 
vical vertebra;  q,  ulna; 
10,    humerus;     //,    radius; 

12,  carpo-metacarpus; 

13,  first  phalanx  of  second 
digit;  14,  third  digit;  75,  sec- 
ond digit;  16,  ilium;  77,  ilio- 
ischiatic  foramen;  18,  pygo- 
style;  ip,  femur;  20,  tibio- 
tarsus;  21,  fibula;  22,  patella; 
23,  tarso-metatarsus;  24,  first 
toe;  25,  second  toe;  26,  third 
toe;  27,  fourth  toe;  28,  spur; 
2Q,  pubis ;  30,  ischium ; 
31,    clavicle ;     32,    coracoid ; 


33,  keel  of  Sternum;    34.  xiphoid  process.      (From  Shipley  and  MacBride.) 


CLASS   AVES  581 

use  this  organ  as  a  rudder  while  flying  and  as  a  balancer  while 
perching. 

There  are  tw^o  cervical  ribs  and  five  thoracic  ribs  on  each  side. 
The  second  cervical  and  first  four  thoracic  ribs  bear  each  an 
uncinate  process  which  arises  from  the  posterior  margin  and 
overlaps  the  succeeding  rib,  thus  making  a  firmer  framework. 
The  thoracic  ribs  are  connected  with  the  sternum  or  breastbone. 
The  sternum  is  united  in  front  with  the  coracoid  (Fig.  474,  32) 
of  the  pectoral  girdle  and  bears  on  its  ventral  surface  a  large 
crest  or  keel  {carina,  Fig.  474,  jj)  to  which  the  muscles  that  move 
the  wings  are  attached. 

The  pectoral  girdle  consists  of  a  pair  of  blade-like  scapula, 
the  shoulder-blades,  which  lie  above  the  ribs  one  on  either  side 
of  the  vertebral  column  in  the  thorax.  The  coracoids  (Fig.  474, 
j2)  connect  the  sternum  with  the  anterior  end  of  the  scapulae 
at  the  shoulders.  A  concavity  in  these  bones  at  their  junction 
furnishes  the  articular  surface  for  the  long  wing  bone  (humerus), 
and  is  called  the  glenoid  cavity.  The  two  clavicles  (Fig.  474,  ji) 
connect  proximally  with  the  shoulder  and  are  fused  together 
distally,  forming  a  V-shaped  furcula  or  "  wishbone."  The 
clavicles  are  homologous  to  the  collar-bones  of  man,  and  serve 
to  brace  the  shoulders. 

The  fore  limb  or  wing  of  the  pigeon  (Fig.  471)  is  greatly 
modified.  There  are  but  three  digits,  and  only  one  of  these  is 
well  developed.  The  distal  row  of  carpal  bones  and  the  three 
metacarpals  are  fused  together  forming  a  carpo-metacarpus 
(Fig.  471,  Mi-Mj) ;  this  adds  to  the  rigidity  of  the  wing.  The 
arm  contains,  as  in  other  vertebrates,  a  single  bone,  the  humerus 
(X),  with  a  convex  head  which  lies  in  the  glenoid  cavity.  The 
fore  arm  possesses  two  bones,  the  radius  (F)  and  ulna  (Z). 
The  wrist  contains  two  carpal  bones  {UC  and  RC);  the  other 
carpal  bones  are  fused  with  the  three  metacarpals  (Mi-Mj), 
forming  the  carpo-metacarpus,  as  stated  above.  Besides  the 
carpo-metacarpus,  the  hand  possesses  a  preaxial  digit  with  two 
small  bones  (Ni),  which  supports  a  small  tuft  of  feathers  and 


582  COLLEGE  ZOOLOGY 

is  known  as  the  bastard  wing  {BW))  a  middle  digit  with  three 
phalanges  {O1-O2);  and  a  postaxial  digit  (Ri)  containing  a 
single  phalanx. 

The  pelvic  girdle  consists  of  the  ilia  (Fig.  474, 16),  the  ischia  (30), 
and  the  pubes  (2p),  as  in  nearly  all  of  the  vertebrates  above  the 
fishes.  These  bones  are  firmly  fused  together  and  united  with 
the  posterior  part  of  the  vertebral  column  in  the  trunk  which 
is  called  the  sacrum.  At  their  junction  on  either  side  is  a  con- 
cavity, the  acetabulum,  in  which  the  head  of  the  thigh-bone  fits. 

The  hind  limbs  are  used  for  bipedal  locomotion.  The  thigh 
is  concealed  beneath  the  feathers.  The  femur  (Fig.  474,  ig)  is 
the  short,  thick,  thigh-bone.  In  the  leg  are  the  slender  fibula 
(21),  and  the  long,  stout  Hbiotarsus  (20)  'which  consists  of  the 
tibia  fused  with  the  proximal  row  of  tarsal  bones.  The  ankle- 
joint  is  between  the  tibiotarsus  (20)  and  the  tar  so -metatarsus 
(23) ;  the  latter  represents  the  distal  row  of  tarsal  bones  and  the 
second,  third,  fourth,  and  fifth  metatarsals  fused  together.  The 
foot  possesses,  besides  the  tarso-metatarsus,  four  digits  ;  the  first 
is  directed  backwards  and  is  called  the  hallux  {24) ;  and  the  other 
three  (25,  26,  27)  are  directed  forwards.  Each  digit  bears  a 
terminal  claw.  The  tarso-metatarsus  of  the  fowl  bears  a  back- 
wardly  directed  spur  {28). 

The  Muscular  System.  —  The  muscles  of  the  neck,  tail,  wings, 
and  legs  are  especially  well  developed.  Those  that  produce  the 
downward  stroke  of  the  wings,  the  pectoral  muscles,  are  the  largest; 
they  weigh  about  one  fifth  as  much  as  the  entire  body;  they 
take  their  origin  from  the  sternum  and  its  keel,  and  constitute 
what  is  popularly  known  as  the  "  breast  "  of  the  bird.  Con- 
nected with  the  leg  muscles  is  a  mechanism  which  enables  the  bird 
to  maintain  itself  "upon  a  perch  even  while  asleep.  If  the  hind 
limb  is  bent,  a  pull  is  exerted  on  a  tendon  which  flexes  all  of  the 
toes  and  bends  them  automatically  round  the  perch.  When 
resting,  the  mere  weight  of  the  body  bends  the  hind  limb  and  con- 
sequently causes  the  toes  to  grasp  the  perch  and  hold  the  bird 
firmly  in  place. 


CLASS  AVES  583 

The  Digestive  System.  —  Pigeons  feed  principally  upon 
vegetable  food,  such  as  seeds.  The  mouth  cavity  opens  into  the 
oesophagus  (Fig.  471,  C),  which  enlarges  into  a  crop  (D) ;  here  the 
food  is  macerated.  The  stomach  consists  of  two  parts,  an  an- 
terior proventriculus  (/)  with  thick  glandular  walls,  which 
secretes  the  gastric  juice,  and  a  thick  muscular  gizzard  {K), 
which  grinds  up  the  food  with  the  aid  of  small  pebbles  swallowed 
by  the  bird.  The  intestine  forms  a  U-shaped  loop,  the  duodenum 
(M),  which  leads  into  the  coiled  small  intestine,  or  ileum,  and 
finally  passes  into  the  rectum  (R)  at  a  point  where  two  blind 
pouches,  the  cceca  (T),  are  given  off.  The  aHmentary  canal  leads 
into  the  cloaca  into  which  the  urinary  and  genital  ducts  also  open. 
The  cloaca  opens  to  the  outside  by  means  of  the  anus  (iY).  In 
young  birds  a  thick  glandular  pouch,  the  bursa  Fabricii  (O), 
lies  just  above  the  cloaca. 

The  two  bile  ducts  {Hi,  H2),  one  from  each  lobe  of  the  liver 
{L),  discharge  the  bile  into  the  duodenum.  There  is  no  gall- 
bladder. The  pancreas  (F)  pours  its  secretions  into  the  duo- 
denum through  three  ducts  (Fi,  F2,  Fj).  There  is  a  spleen, 
paired  thyroids,  adrenal  bodies,  and,  in  young  pigeonSj  paired 
thymus  glands  (see  p.  492). 

The  Circulatory  System  (Fig.  475).  — The  heart  of  a  bird  is 
comparatively  large.  It  is  composed  of  two  entirely  separated 
muscular  ventricles  {l.vn,  r.vn)  and  two  thin- walled  auricles  (l.au, 
r.au).  The  right  auricle  (r.au)  receives  impure,  venous  blood 
from  the  right  precaval  (r.prc),  the  left  precaval  (l.prc),  and  the 
postcaval  veins  (ptc).  This  blood  passes  from  the  right  auricle 
into  the  right  ventricle  (r.vn),  and  is  then  pumped  through 
the  pulmonary  artery,  which  divides  into  right  (r.p.a)  and 
left  (l.p.a)  pulmonary  arteries,  leading  to  the  right  and  left 
lungs  respectively. 

The  left  auricle  (Fig.  475,  l.au)  receives  the  blood  which 
returns,  after  being  aerated  in  the  lungs,  through  four  large 
pulmonary  veins.  It  passes  from  the  left  auricle  into  the  left 
ventricle,  and  is  then  pumped  through  the  right  aortic  arch 


584 


COLLEGE  ZOOLOGY 


SCO- 


Fig.  475— The  heart 
and  chief  blood-vessels  of 
the  pigeon,  ventral  as- 
pect, a.ao,  aortic  arch; 
a.m.a,  anterior  mesenteric 
artery ;  a.r.v,  afferent 
renal  veins;  a.r.v',  vein 
bringing  blood  from  pelvis 
into  renal  portal  system; 
br.a,  brachial  artery; 
br.  V,  brachial  vein;  c,  cau- 
dal artery  and  vein ; 
c.c,  common  carotid 
artery  ;  c.m.v,  coc- 
cygeo-mesenteric  vein ; 
coe.a,  coeliac  artery ; 
d.ao,  dorsal  aorta;  e.c, 
external  carotid  artery ; 
epg,  epigastric  vein; 
e.r.v,  efferent  renal  vein; 
f.a,  femoral  artery; 
f.v,  femoral  vein;  h.v,  he- 
patic vein;  i.c,  internal 
carotid  artery;  i.il,  in- 
ternal iliac  artery  and 
vein;  i.m,  internal  mam- 
mary artery  and  vein ; 
in.a,  innominate  artery; 
i.v,  iliac  vein;  ju,  jugular 
vein;  ju',  anastomosis  of 
jugular  veins;  l.au,  left 
auricle;  l.p.a,  left  pul- 
monary artery;  l.pre,\eit 
precaval  vein;  l.vn,  left 
ventricle;  pc,  left  pectoral 
arteries  and  veins; 
pea,  right  pectoral  ar- 
tery; pc.v,  right  pectoral 
vein ;  p.tn.a,  posterior 
mesenteric  artery; 
ptc,  postcaval  vein;  ra.i, 
ra.2,  ra.3,  renal  arteries; 
r.au,  right  auricle ; 
r.p.v,  renal  portal  vein ; 
r.p.a,  right  pulmonary 
artery;  r.pr.v,  right  pre- 
caval vein ;  r.v,  renal 
vein;  t.vn,  right  ven- 
tricle ;  sea,  sciatic  ar- 
tery ;  sc.v,  sciatic  vein ; 
scl.a,  subclavian  artery; 
vr,  vertebral  artery  and 
vein.  (From  Parker  and 
Haswell,  after  Parker.) 


CLASS  AVES  585 

(a.ao),  which  gives  off  the  innominate  arteries  (m.a)  and  then 
continues  as  the  dorsal  aorta  (d.ao). 

Contrasting  the  circulatory  system  of  the  pigeon  with  that 
of  the  turtle,  it  should  be  noted  that  the  venous  blood  and  arterial 
blood  are  not  allowed  to  mingle  in  the  heart  of  the  pigeon.  The 
renal  portal  system  *of  the  pigeon  fias  almost  completely  dis- 
appeared, the  blood  being  taken  from  the  posterior  part  of  the 
body  directly  to  the  heart,  and  not  through  the  renal  capillaries, 
as  in  all  lower  vertebrates.  The  jugular  veins  (Fig.  475,  ju)  of 
the  pigeon  are  united  just  under  the  head  by  a  cross  vein  (ju') ; 
this  enables  blood  to  pass  back  to  the  heart  from  the  head  when 
the  neck  becomes  momentarily  twisted  so  that  one  of  the  jugular 
veins  is  stopped  up. 

The  Respiratory  System.  —  The  two  lungs  in  birds  are  as- 
sisted by  a  remarkable  system  of  air-sacs.  During  inspiration, 
the  relaxation  of  the  thoracic  and  abdominal  muscles  allows 
the  elastic  expansion  of  the  thorax  and  abdomen.  Air  enters 
the  mouth  cavity  through  the  nostrils,  as  in  reptiles;  it  then 
passes  through  the  glottis  into  the  trachea  or  windpipe,  which 
divides,  sending  a  branch  {bronchus)  to  each  lung.  The  bronchi 
communicate  with  nine  large  thin-walled  air-sacs,  which  lie 
principally  along  the  sides  and  dorsal  surface  of  the  body-cavity. 
During  expiration,  the  muscles  of  the  thorax  and  abdomen  con- 
tract, forcing  the  air  from  the  air-sacs,  through  the  limgs  and 
trachea,  and  out  of  the  nostrils.  At  each  inspiration  practically 
all  of  the  air  in  the  lungs  is  renewed. 

The  air-sacs  enable  the  bird  to  breathe  easily  when  in  flight, 
since  air  is  forced  into  them  during  the  rapid  progress  through 
the  atmosphere  and  out  of  them  by  the  compression  of  the 
pectoral  muscles,  which  lower  the  wings.  In  man,  violent  move- 
ments interfere  with  the  alternate  inspiration  and  expiration  of 
air. 

The  trachea  is  held  open  by  partially  ossified  cartilaginous 
rings.  Where  the  trachea  divides  into  the  two  bronchi,  it  en- 
larges to  form  the  vocal  organ,  or  syrinx,  a  structure  peculiar  to^ 


586  COLLEGE  ZOOLOGY 

birds.  Extending  forward  from  the  angle  of  bifurcation  of  the 
trachea  is  a  flexible  valve  which  is  vibrated  when  air  is  forcibly 
expelled  from  the  lungs,  thus  producing  a  sound.  A  number  of 
muscles  are  able  to  alter  the  tension  of  this  valve  and  conse- 
quently the  number  of  its  vibrations  and  the  pitch  of  the  note 
produced. 

The  Excretory  System.  — The  kidneys  are  a  pair  of  three-lobed 
bodies  situated  as  shown  in  Figure  471,  U.  Each  discharges 
its  secretion,  the  urine,  through  a  duct,  the  ureter  (S),  into  the 
cloaca.  There  is  no  urinary  bladder ,  but  the  urine  passes  directly 
out  of  the  anus  with  the  faeces. 

The  Reproductive  System.  —  In  the  male  are  a  pair  of  oval 
testes.  From  each  testis  a  duct,  the  vas  deferens,  passes  back 
and  opens  into  the  cloaca;  it  dilates  at  its  distal  end  to  form 
a  seminal  vesicle.  The  spermatozoa  pass  through  the  vasa  def- 
erentia;  are  stored  in  the  seminal  vesicles;  and,  when  copula- 
tion takes  place,  are  discharged  into  the  cloaca,  and  transferred 
by  contact  to  the  cloaca  of  the  female.  There  is  no  copulatory 
organ. 

The  right  ovary  of  the  female  disappears  during  development 
and  only  the  left  ovary  persists  in  the  adult.  The  ova  break 
out  of  the  ovary  and  enter  the  oviducts.  During  their  passage 
through  the  oviducts  the  albuminous  substance,  known  as  the 
"  white  "  of  the  egg,  is  secreted  about  them  by  the  walls  of  the 
middle  portion.  The  double,  parchment-like  shell-membrane 
is  then  secreted  about  the  egg,  and  finally  the  shell  is  added  by 
the  posterior  part  of  the  oviduct  a  short  time  before  deposition. 

Fertilization  takes  place  about  forty-one  hours  before  the 
eggs  are  laid.  Two  eggs  are  laid  by  pigeons  at  a  sitting,  the 
first  usually  between  four  and  six  p.m.,  and  the  second  between 
one  and  two  p.m.,  two  days  later.  They  are  kept  at  a  temper- 
ature of  about  100°  F.  by  the  sitting  bird  for  usually  fourteen 
days.  At  the  end  of  this  period  of  incubation,  the  young  birds 
have  developed  to  such  a  stage  that  they  are  able  to  break 
through  the  shell,  i.e.  they  hatch.     They  are  at  first  covered  with 


CLASS  AVES 


587 


fine  down,  but  soon  acquire  a  covering  of  contour  feathers. 
During  their  early  Hfe  as  nesthngs  they  are  fed  upon  "  pigeon's 
milk,"  a  secretion  from  the  crop  of  the  adult. 

The  Nervous  System.  —  The  brain  of  the  pigeon  (Fig.  476) 
is  very  short  and  broad.  The  cerebellum  (cb)  is  comparatively 
large,  as  are  also  the  optic  lobes  (o.l),  showing  that  birds  have 


^^^^umi^X 


Fig.  476.  —  The  brain  of  the  pigeon,  si«le  view,  cb,  cerebellum;  c.h,  cerebral 
hemispheres;  /,  flocculus;  m.o,  medulla  oblongata;  o.l,  optic  lobes;  o.t,  optic 
tracts;  pn,  pineal  body;  II-XII,  cerebral  nerves.     (From  Parker  and  Haswell.) 

well-developed  powers  of  coordination  and  of  sight.  The  ol- 
faciory  lobes  (olf),  on  the  other  hand,  are  very  small,  indicating 
poorly  developed  olfactory  organs. 

The  Sense-organs.  —  The  bill  and  tongue  serve  as  tactile 
organs.  Tactile  nerves  are  also  present  at  the  base  of  the  feathers, 
especially  those  of  the  wings  and  tail.  Birds  are  unable  to  dis- 
tinguish delicate  odors,  and  on  the  whole  their  sense  of  smell  is 
very  poor.  The  sense  of  taste  is  also  very  poorly  developed, 
but  is  nevertheless  present,  as  can  easily  be  proved  if  a  bad- 
tasting  morsel  of  food  is  presented  to  a  bird. 

The  cochlea  of  the  ear  is  more  complex  than  that  of  reptiles. 
The  Eustachian  tubes  open  by  a  single  aperture  on  the  roof  of  the 
pharynx.  Birds  have  acute  and  discriminating  powers  of  hear- 
ing —  a  power  correlated  with  their  singing  ability. 

The  eyes  of  birds  are  very  large,  and  have  a  biconvex  shape. 
They  are  surrounded  by  bony  sclerotic  plates,  and  contain  a  fan- 


588  COLLEGE  ZOOLOGY 

shaped,  highly  vascular,  pigmented  structure  called  the  pecten, 
which  is  suspended  in  the  vitreous  humor.  The  function  of  the 
pecten  is  uncertain ;  it  may  have  some  connection  with  the  nutri- 
tion of  the  eyeball,  or  with  the  process  of  accommodation.  The 
latter  process  is  remarkably  well  developed  in  birds,  since  their 
eyes  are  equally  adapted  both  for  far  and  near  vision,  and  a  bird 
can  fly  rapidly  among  the  branches  of  a  tree  without  striking  a 
branch,  or  can  swoop  down  to  the  ground  from  a  great  height  in  the 
air,  changing  from  far-sighted  to  near-sighted  vision  in  an  instant. 

2.  A  Brief  Classification  of  Birds 

The  birds  form  a  more  homogeneous  class  of  vertebrates  than 
the  reptiles  and  cannot  be  separated  into  a  few  well-defined 
groups.  There  are  comparatively  few  fossil  birds  known  to 
man;  in  fact,  only  one  subclass,  containing  a  single  genus,  and 
four  orders,  are  not  represented  by  living  forms.  The  structural 
differences  that  distinguish  the  orders,  families,  genera,  and 
species  are,  for  the  most  part,  so  slight  as  to  make  it 
impossible  to  state  them  in  a  brief  and  clear  manner. 

More  than  twelve  thousand  species  of  birds  have  been  de- 
scribed, and  no  two  authorities  agree  as  to  their  classification. 
The  following  arrangement  is  adopted  from  Knowlton's  Birds 
of  the  World. 

Class  Aves.  Birds.  —  Warm-blooded  vertebrates  with 
feathers;  usually  with  fore  Hmbs  adapted  for  flight;  the  adults 
of  existing  species  without  teeth. 

Subclass  I.  Arcileornithes.  —  Ancient,  reptile-like,  fossil 
birds.  Only  three  specimens  of  the  single  genus  Archceopteryx 
are  known. 

Subclass  II.  Neornithes.  —  Recent  Birds.  —  There  are 
four  orders  containing  only  extinct  forms,  and  seventeen  orders 
containing  living  representatives. 

Order  i.  Hesperornithiformes. — Fossil,  toothed-birds  from 
America,  with  teeth  set  in  a  groove.  Example:  Hesperornis 
(Fig.  478). 


CLASS  AVES  589 

Order  2.  Ichthyornithiformes.  —  Fossil,  toothed-birds  from 
America,  with  teeth  set  in  separate  sockets.  Example:  Ich- 
thyornis   (Fig.   479). 

Order  3.  Struthioniformes.  —  Ostriches.  —  Flightless,  ter- 
restrial birds  with  naked  head,  nedk,  and  legs;  feet  with  two 
toes;  without  pygostyle;  no  keel  on  sternum.  Example: 
Struthio,  African  Ostrich  (Fig.  480). 

Order  4.  Rheif ormes.  —  Rheas.  —  Flightless,  terrestrial  birds 
with  partially  feathered  head  and  neck;  feathers  without  after- 
shaft;  feet  with  three  toes.  Example:  Rhea,  American  Ostrich 
(Fig.  481). 

Order  5.  Casuariiformes.  —  Cassowaries  and  Emeus.  — 
FHghtless  terrestrial  birds  with  very  small  wings;  feathers  with 
large  aftershaft.  Examples:  Casuarius,  Cassowary;  DromceuSj 
Emeu  (Fig.  482). 

Order  6.  Crypturifonnes.  —  Tinamous.  —  Flying,  terrestrial 
birds,  with  short  tail;  no  pygostyle.     Example:   Tinamus  (Fig. 

483). 

Order  7.  Dinornithiformes.  —  MoAS.  —  Flightless,  terrestrial 
birds,  with  enormous  hind  limbs;  wing  bones  absent;  all  extinct. 
Example:  Dinornis  (Fig.  484). 

Order  8.  ^pyomithifonnes. — Elephant-birds. — Flightless, 
terrestrial  birds,  with  enormous  hind  limbs;  sternum  and  wings 
small;  eggs  very  large ;  all  extinct.     Example:  jEpyornis. 

Order  9.  Apterygiformes.  —  Kiwis.  —  Flightless  terrestrial 
birds;  feathers  hair-like  and  without  aftershaft;  all  small  in 
size.     Example:    Apteryx  (Fig.  485). 

Order  10.  Spheniscif ormes.  —  Penguins.  —  Flightless  marine 
birds,  with  small,  scale-like  feathers  ;  wings  modified  as 
paddles  for  swimming;  one  family.  Example:  Spheniscus 
(Fig.  486). 

Order  11.  Colymbif ormes.  — Loons  and  Grebes.  — Aquatic 
birds  with  webbed  or  lobed  toes;  feet  far  back;  body  carried 
upright;  two  suborders  and  two  families.  Examples:  Gaviaj 
Loon  (Fig.  487);    Dytes,  Grebe. 


590  COLLEGE   ZOOLOGY 

Order  12.  Procellariiformes. — Albatrosses  and  Petrels. — 
Marine  birds  with  webbed  toes;  powers  of  flight,  great;  sheath 
of  bill  of  several  pieces;  three  families.  Examples:  Diomedea, 
Albatross  (Fig.  488);   Procellaria,  Petrel  (Fig.  489). 

Order  13.  Ciconiiformes.  —  Stork-like  Birds.  —  Aquatic  or 
marsh-birds  with  feet  adapted  for  wading;  four  suborders,  one 
superfamily,  and  thirteen  families.  Examples:  Pelecanid^, 
Pelicans;  Phalacrocoracid^,  Cormorants  (Fig.  490);  An- 
HiNGiD^,  Snake-birds;  Ardeid/E,  Herons;  iBiDiDiE,  Ibises; 
PHCENicoPTERiDiE,  Flamingos  (Fig.  491). 

Order  14.  Anseriformes.  —  Goose-like  •  Birds.  —  Aquatic 
birds  with  beak  covered  by  a  soft,  sensitive  membrane  and  edged 
with  horny  lamellae ;  two  suborders  and  two  families.  Examples : 
PALAMEDEID.E,  Screamers;  Anatid^,  Swans,  Geese,  and 
Ducks  (Fig.  492). 

Order  15.  Falconiformes. — Falcon-like  Birds. — Carniv- 
orous birds  with  curved  beak,  hooked  at  the  end;  feet  adapted 
for  perching  and  provided  with  strong,  sharp  claws;  three  sub- 
orders and  four  families.  Examples:  CATHARTiDiE,  American 
Vultures;  Gypogeranid^e,  Secretary-birds;  FALCONiDiE,  Falcons; 
BuTEONiDiE,  Eagles,  Hawks,  Vultures,  etc.  (Figs.  493-495). 

Order  16.  Galliformes.  —  Fowl-like  Birds.  — ^^  Terrestrial  or 
arboreal  birds  with  feet  adapted  for  perching;  four  suborders  and 
seven  families.  Examples:  Phasianid^,  Turkeys,  Quails, 
Pheasant,  etc.:  QpiSTHOCOMiDiE,  Hoactzin. 

Order  17.  Gruiformes.  —  Crane-like  Birds. — Mostly  marsh 
birds;  seven  families.  Examples:  Rallid^,  Rails;  Gruid^e, 
Cranes. 

Order  18.  Charadriiformes. — Plover-like  Birds. — Terres- 
trial, arboreal,  or  marine  birds;  four  suborders  and  twelve 
families.  Examples:  Charadriid.'E,  Plovers,  Snipes,  and 
Curlews;  Larid^e,  Gulls  and  Terns  (Fig.  497);  Alcid^,  Auks 
(Fig.  498);   CoLUMBiD^,  Pigeons  (Fig.  470). 

Order  19.  Cuculiformes.  —  Cuckoo-like  Birds. — Arboreal 
birds  with  first  and  fourth  toes  directed  backwards;   fourth  toe 


CLASS  AVES 


591 


may  be  reversible;  two  suborders  and  four  families.  Examples: 
CucuLiD^,  Cuckoos  (Fig.  499);  PsixxACiDiE,  Cockatoos  and 
Parrots. 

Order  20.  Coraciiformes. — Roller-like  Birds. — Arboreal 
birds  with  short  legs;  seven  suborders  and  eighteen  famiHes. 
Examples:  Coraciid^,  Rollers;'  Alcedinid^,  Kingfishers 
(Fig.  500);  SxRiGiDiE,  Owls  (Fig.  501);  Caprimulgid^,  goat- 
sucker^; Trochilid^,  Humming-birds  (Fig.  502);  Micro- 
PODiD^,  Swifts;    PiciD^,  Woodpeckers  (Fig.  503). 

Order  21.  Passeriformes.  —  Sparrow-like  Birds. — More 
than  half  of  all  the  birds  known  belong  to  this  order.  There 
are  two  suborders,  four  superfamilies,  and  sixty-four  families. 
The  twenty- five  North  American  families  are  as  follows:  — 

Family  Common  Name 

1.  Tyrannid^   ....  Tyrant  Flycatchers  (Fig.  504,  A) 

2.  CoTiNGiD^     ....  Cotingas 

3.  Alaudid^ Larks 

4.  MoTACiLLiD^  .  .  .  Wagtails 

5.  TuRDiD^ Thrushes,  Bluebirds,  etc. 

6.  MiMiD^ Thrashers,  Mocking-birds,  etc.  (Fig. 

504,  H) 

7.  CiNCLiD.^. Dippers 

8.  Troglodytid,^    .  .  Wrens   (Fig.   504,   G) 

9.  Cham^id^    ....  Wren-Tits 

10.  Sylviid.^ Warblers,  Kinglets,  and  Gnatcatchers 

11.  HiRUNDiNiD/E  .   .  .  Swallows  (Fig.  504,  E) 

12.  BoMBYCiLLiD^    .   .  Waxwings  (Fig.  504,  F) 

13.  Ptilogonatid^  .  .  Silky  Flycatchers 

14.  LANIID.E Shrikes 

15.  ViREONiD.E    ....  Vireos 

16.  SiTTiD^ Nuthatches 

17.  Parid^ Titmice 

18.  CoRViD^ Crows,  Jays,  etc.  (Fig.  504,  B) 

19.  Sturnid^      :      ,  ,  Starlings 


592 


COLLEGE  ZOOLOGY 


Fig.  477.  —  ArchcEopteryx  Uthographica.  c,  carpal;  c/,  furcula;  co,  coracoid; 
h,  humerus;  r,  radius;  sc,  scapula;  «,  ulna;  I-IV,  digits.  (From  Zittel,  after 
Steinmann  and  Doderlein.) 


CLASS  AVES 


593 


Family 

20.  Certhiid^    . 

21.  CCEREBID^      . 

22.  MnIOTILTID^ 

23.  Tanagrid^  . 

24.  icterid.e  .  . 

25.  FRINGILLIDiE 


Common  Name 
Creepers 
Honey  Creepers 
Wood  Warblers 
Tanagers 

Blackbirds,  Orioles,  etc.  (Fig.  504,  C) 
Finches,  Sparrows,  etc.  (Fig.  504,  D) 


3.   A  Review  of  the  Orders  and  Families  of  Birds 

It  is,  of  course,  impossible  in  the  limited  space  that  can  be 
devoted  to  birds  in  this  book  to  give  anything  more  than  a  brief 
survey  of  the  subject.  Most  of  the  families  that  are  considered 
are  represented  by  living  species  inhabiting  the  United  States. 

Subclass  I.  ARcaaEORNiTHES.  —  The  single  genus,  ArchcE- 
opteryx  (Fig.  477),  belonging  to  this  subclass  is  known  from 
a  feather  and  two 
fairly  complete 
skeletons  that  were 
found  in  the  litho- 
graphic slates  of 
Solenhofen,  Bavaria, 
of  the  Upper  Juras- 
sic period.  Archce- 
opteryx  was  about 
the  size  of  a  crow. 
It  possessed  teeth 
embedded  in  sockets, 
fore  limbs  with  three 
clawed  digits  (Fig. 
477,  I,  n,  III)  and 
separate  metacarpal 
bones,  and  a  lizard- 
like tail  with  large 
feathers  (rectrices) 
on  either  side.     The 

2Q 


Fig.  478. 


H'sperornis  regalis. 
after  Marsh.) 


(From  Zittel, 


594 


COLLEGE   ZOOLOGY 


bird-like  characteristics  predominate  over  the  reptilian  features 
so  that  this  curious  creature  is  placed  in  the  class  Aves,  although 
it  is  a  connecting  link  between  the  birds  and  the  reptiles. 
Subclass  II.   Neornithes.  —  Recent  Birds. 
Order  i.   Hesperornithiformes. — There  are  three  species  of 
fossil  birds  in  this  order.    Hesperornis  regalis  (Fig.  478),  the  best- 
known   species,  was 
nearly   four  feet  in 
length.    It  possessed 
teeth  set  in  a  groove, 
strong    hind     limbs 
with    webbed    feet, 
which  were  used  like 
oars,  and  a  sternum 
without  a  keel.    The 
entire  anatomy  indi- 
cates that  Hesperor- 
nis was  a  flightless, 
swimming  and  diving 
bird  which  lived  upon 
fishes   and    other 
aquatic    animals. 
The  remains  of  this 
and   the    two   other 
species  probably  be- 
longing to  this  order 
were    found    in   the 
Cretaceous   deposits 
of  Kansas. 
Order  2.    Ichthyornithiformes.  —  Of    the    dozen    or     more 
species  of  fossil  birds  included  in  this  order,  Ichthyornis  victor 
(Fig.  479)  from  the  Cretaceous  deposits  of  Kansas,  is  the  best 
known.     This  bird  had  teeth  set  in  sockets,  a  keeled  sternum, 
and  well-developed  wings.     It  w^as  about  the  size  of  a  pigeon, 
was  a  strong  flier,  and  probably  fed  upon  fish. 


Fig. 


479.  — Ichthyornis  victor. 
after  Marsh.) 


(From  Zittel, 


CLASS  AVES 


595 


Order  3.  Struthioniformes.  —  Ostriches. — The  ostriches  are 
the  largest  living  birds,  attaining  a  height  of  more  than  eight 
feet,  and  a  weight  of  over  three  hundred  pounds.  Four  species 
are  recognized  by  some  authorities.  The  ostriches  or  camel 
birds  of  North  Africa,  Struthio  camdus  (Fig.  480),  live  in  desert 
regions  and  travel  about  in  groups,  usually  of  from  four  to  twenty. 
They  are  very  suspicious  and  flee  from  any  signs  of  danger. 
They  do  not  stick  their  heads  in 
the  sand  and  think  themselves 
hidden,  as  commonly  reported. 
Their  speed  is  remarkable,  reach- 
ing sixty  miles  an  hour,  and  their 
single  strides  may  measure  more 
than  twenty- five  feet.  They  are 
omnivorous,  feeding  upon  many 
kinds  of  plants  and  animals. 
The  nest  is  a  hollow  in  the 
sand,  and  several  females  lay 
their  eggs  in  a  single  nest.  Each 
egg  weighs  from  three  to  four 
pounds.  The  males  do  most  of 
the  incubating.  The  young, 
which  appear  in  six  or  seven 
weeks,  run  about  as  soon  as 
they  emerge  from  the  shell. 

Ostrich  feathers  are  now 
procured  almost  entirely  from 
domesticated    birds.      In    1904 

there  were  in  South  Africa  over  three  hundred  and  fifty 
thousand  tame  ostriches  which  yielded  an  annual  income 
of  about  $18  each.  Ostrich  farming  is  now  successfully 
carried  on  in  California,  Arizona,  Arkansas,  North  Caro- 
lina, and  Florida.  The  feathers  are  clipped  without  pain 
to  the  birds;  those  from  a  single  adult  weigh  about  one 
pound. 


Fig.  480.  —  Ostrich,  Struthio  camelus. 
(From  Evans.) 


596 


COLLEGE  ZOOLOGY 


Fig,  481.  —  Rhea,  Rhea  americana. 
Evans.) 


(From 


Order  4.  Rhei- 
formes.  —  Rheas.  — 
These  are  the  New- 
world  ostriches  (Fig. 
481).  There  are  three 
species  inhabiting  the 
pampas  of  South 
America.  They  are 
smaller  than  the  true 
ostriches,  but  their 
habits  are  quite  similar. 
Order  5.  Casuari- 
iformes.  —  Casso- 
WARiES  and  Emeus.  — 
The  two  families  in 
this    order    contain 

ostrich-like  birds;   the  Drom^eid^e  or  emeus  (Fig.  482),  which 

are,  next  to  the  ostriches,  the  largest  of  living  birds,  are  confined 

to  Australia ;    the  CASUARiiDiE  or 

cassowaries    inhabit    New    Guinea 

and  neighboring  islands.     The  cas- 
sowaries  usually   possess   a   bony, 

helmet-like  knot  on  the  head,  and 

have  brightly  colored  lobes  on  the 

head  and  neck;  these  are  absent  in 

emeus. 

Order  6.   Crypturiformes.  — Tin- 

AMOUS.  —  About    forty   species   of 

tinamous    are    known.     They    re- 
semble  game-birds   in   appearance 

and  are  called  partridges  by  the 

natives   of    southern   Mexico   and 

Central  and  South  America,  where 

they  live.      The  powers  of  flight  of     YlG.4S2.-Emeu,Dromceusnov^ 
the    tinamous    are    not  well    devel-  hollanduB.     (From  Evans.) 


CLASS  AVES 


597 


oped.  In  size  they  range  from  a  length  of  six  inches  to  that  of 
the  rufous  or  great  tinamou,  Rhynchotus  rufescens  (Fig.  483), 
of  Brazil,  which  is  fourteen  inches  long.  Tinamous  are  solitary 
birds,  but  may  band  together  into  coveys.  They  make  a  nest 
by  scratching  a  hollo-w- 
in the  earth  and  lining  ^^^^^ 
it  -with  grasses,  leaves, 
and  feathers.  The 
eggs  number  from  five 
to  a  dozen  or  more 
to  a  setting;  they  are 
incubated  by  the 
male. 


Fig.  483.  —  Great  tinamou,  Rhyn-      Fig.  484.  —  Moa,  Palapteryx  elephan- 
chotus  rufescens.     (From  Evans.)  topus.     (From  Zittel,  after  Owen.) 


Order  7.  Dinornithiformes.  —  MoAS  (Fig.  484).  —  The  moas 
have  probably  become  extinct  -within  the  past  five  hundred  years. 
The  remains  of  these  peculiar  birds  have  been  found  in  great 
numbers  in  caves  and  refuse  heaps  in  Ne-w  Zealand,  to  -which 
country  they  appear  to  have  been  confined.  Twenty  or  thirty 
specie^  are  known  from  these  remains.     They  ranged  in  size  from 


598 


COLLEGE   ZOOLOGY 


that  of  a  turkey  to  nearly  ten  feet  high.     They  were  flightless, 
but  possessed  enormous  hind  limbs. 

Order  8.  iEpyornithiformes.  —  Elephant-birds.  —  These 
birds  have  probably  become  extinct  within  the  past  five  centuries. 
They  inhabited  Madagascar,  were  flightless,  and  possessed  hind 
limbs  more  enormous  even  than  those  of  the  moas.  Many  of 
their  eggs  have  been  found  in  the  sand  near  the  sea-shore;  they 
are  more  than  thirteen  inches  in  length  and  nine  inches  wide, 
and  have  a  capacity  of  over  two  gallons. 

Order  9.  Apterygiformes.  —  Kiwis.  —  These  wingless  birds 
of  New  Zealand  belong  to  the  single  genus  Apteryx  (Fig.  485) 

and  to  five  or  six 
species.  They  are 
about  the  size  of  a 
common  fowl;  their 
wings  are  aborted, 
and  they  lack  tail- 
feathers.  In  habit, 
they  are  nocturnal, 
feeding  upon  worms, 
which  they  probe 
for  with  their  long 
beaks,  and  also  upon 
vegetable  matter.  The  nest  is  made  in  a  hole  in  the  ground, 
and  one  or  two  large  eggs  are  laid. 

Order  10.  Sphenisciformes. — Penguins. — The  penguins,  of 
which  about  twenty  living  species  are  known,  are  confined  to 
the  rocky  and  barren  islands  of  the  Antarctic  region.  They  are 
adapted  for  life  in  the  water;  the  fore  limbs  are  modified  as 
paddles  for  swimming;  the  feet  are  webbed;  the  cold  water 
can  be  shaken  entirely  from  the  feathers;  and  a  layer  of  fat  just 
beneath  the  skin  serves  to  keep  in  the  bodily  heat.  They  feed 
on  fishes  and  other  marine  animals.  On  shore  they  stand  erect 
(Fig.  486),  side  by  side.  They  nest  in  colonies,  laying  the  one 
or  two  eggs  either  among  the  rocks  or  in  a  burrow. 


Fig.  485- 


Kiwi,  Apteryx  australis. 
Evans.) 


(From 


CLASS  AVES 


599 


Fig.  486.  —  Penguins  or  rock-hoppers,  Eudypies  chrysocome.     (From  Evans, 
after  Thomson.) 

Order  1 1 .   Colymbiformes.  —  Loons  and  Grebes. 
Family  Gaviid^.  —  Loons  or  Divers  (Fig.  487). — 'The  one 
genus,  Gavia,  and  five  species  of  loons  inhabit  the  northern  half 


Fig.  487.  —  Loon.     (From  Evans.) 

of  the  northern  hemisphere.  They  are  large  birds  with  strong 
powers  of  flight,  and  with  an  ability  to  swim  and  dive  that  is  not 
surpassed  by  any  other  species.     Loons  are  awkward  on  land. 


6oo 


COLLEGE   ZOOLOGY 


The  two  eggs  are  laid  in  a  slight  depression  in  the  ground,  near 
water. 

Family  Podicipedid^.  —  Grebes. — The  grebes  are  smaller 
than  the  loons,  but  are  excellent  swimmers  and  divers.  There 
are  about  twenty-five  species  in  the  family,  distributed  through- 
out the  world,  chiefly  about  fresh  waters.  The  six  to  eight  eggs 
are  laid  in  a  nest  consisting  usually  of  a  mass  of  floating  rushes. 
Order  12.  Procellariiformes. — Albatrosses  and  Petrels. — • 
These  are  marine  birds  with  tubular  external  nostrils,  fully 

webbed  toes,  and 
long,  narrow  wings. 
They  are  strong 
fliers,  gregarious, 
and  come  to  land 
rarely  except  to 
lay  their  eggs. 
There  are  about 
fifteen  species  of 
albatrosses;  six  of 
these  have  been 
reported  from 
North  America. 
The  wandering  al- 
batross, Diomedea 
exulans  (Fig.  488), 
is  over  three  and 
a  half  feet  in  length,  and  has  a  spread  of  wing  of  over  ten  feet. 
The  petrels,  fulmars,  and  shearwaters,  of  which  there  are 
about  seventy  species,  belong  to  the  family  PROCELLARiiDiE. 
The  fulmars  are  large  gull-like  birds.  The  common  fulmar, 
Fulmarus  glacialis,  is  abundant  in  the  North  Atlantic.  It  lays 
its  single,  white  egg  on  crags  over  the  sea.  The  shearwaters  are 
very  restless  birds  that  inhabit  all  oceans.  The  common  Atlantic 
shearwater  is  Puffinus  major.  The  stormy  petrels  are  small 
birds  under  ten  inches  in  length.     The  common  stormy  petrel, 


Fig.  488. 


Wandering  albatross,  Diomedea  exulans. 
(From  Evans.) 


CLASS  AVES 


6oi 


Procellaria  pelagica  (Fig.  489),  is  known  from  the  Atlantic  and 
Mediterranean  coasts  of  Europe,  Africa,  and  North  America. 


Fig.  489.  —  Stormy  Petrel,  Procellaria  pelagica.     (From  Evans.) 

Order  13.  Ciconiiformes. — Stork-like  Birds. — This  order 
includes  the  tropic  birds,  cormorants,  anhingas,  pelicans,  gan- 
nets,  man-o'-war  birds,  herons,  bitterns,  boatbills,  shoebills, 
hammerheads,  storks,  ibises,  spoonbills,  and  flamingos.  Most 
of  these  birds  have 
long  legs,  long, 
slender  necks, 
elongated  bills, 
and  feet  fitted  for 
wading  or  swim- 
ming. 

The  pelicans 
(Family  Pele- 
CANiD^)  possess 
a  huge  membran- 
ous pouch  between 
the  branches  of  the 

lower  jaw,  with  which  they  scoop  up  small  fish  (Fig.  507,  g). 
The  cormorants   (Family   Phalacrocoracid^)   comprise  the 


Fig.  490. 


Cormorant,  Phalacrocorax  carho. 
(From  Evans.) 


6o2 


COLLEGE  ZOOLOGY 


majority  of  the  species  in  the  order.  They  are  almost  cosmo- 
politan and  very  sociable.  In  China  and  a  few  other  countries 
these  birds  are  trained  to  catch  fish  and  are  of  considerable 
value  to  their  owners.  The  common  cormorant,  or  shag, 
Phalacrocorax  carbo  (Fig.  490),  occurs  on  the  Atlantic  coast  of 

Europe  and  North  America  and 
breeds  on  the  rocky  shores  of 
Labrador  and  Newfoundland. 

The  herons  and  bitterns 
(Family  Ardeid^e)  possess  long 
legs  fitted  for  wading,  broad 
wings,  and  short  tails.  They 
are  found  in  the  warmer  regions 
of  the  globe  and  feed  chiefly  on 
fishes.  The  great  blue  heron, 
Ardea  herodias,  is  a  large  species 
occurring  in  all  parts  of  North 
America.  It  is  about  four  feet 
long  and  has  an  extent  of  wings 
of  about  six  feet.  Its  large  flat 
nest  is  built  of  coarse  sticks 
usually  in  the  top  of  a  high 
tree;  four  to  six  greenish  blue 
eggs  are  laid. 

The  seven  species  of  fla- 
mingos (Family  Phgenicopte- 
RiD^,  Fig.  491)  inhabit  the  tropics ;  one  of  them  occurs  in 
Florida.  They  are  gregarious  birds,  congregating  in  thousands 
on  mud  flats  where  they  build  their  conical  mud  nests.  They 
are  rosy  vermilion  in  general  color. 

Order  14.  Anseriformes.  —  Goose-like  Birds.  — These  birds 
are  either  adapted  for  swimming,  with  short  legs  and  fully 
webbed  front  toes,  or  for  wading,  with  large  feet  and  a  short 
decurved  bill.  Their  young  are  entirely  covered  with  down  and 
can  swim  or  run  about  soon  after  hatching,  i.e,  are  precocious. 


Fig.  491 .  —  Flamingo,  Phoenicopterus 
roseus.     (From  Evans.) 


CLASS  AVES 


603 


The  screamers  (Family  Palamedeid^)  are  all  natives  of  South 
America.  The  family  Anatid^e  contains  about  two  hundred 
and  ten  species  of  duck-like  birds  which  are  aquatic  or  semi- 
aquatic  in  habits,  and  cosmopolitan  in  distribution. 

There  are  five  North  American  subfamilies  of  the  Anatid^: 
(i)  the  swans,  Cygnin.e;  (2)  the  geese,  Anserin^e;  (3)  the  river- 
ducks,  Anatin^e;  (4)  the  sea-ducks,  Fuligulin.'E;  and  (5)  the 
mergansers,  Mergin^e. 

The  most  beautiful  of  all  our  ducks  is  the  wood  duck,  Aix 
sponsa  (Fig.  492).  This  bird  ranges  over  the  entire  United 
States.  Its  favor- 
ite haunts  are  the 
smaller  streams, 
lakes,  and  ponds. 
The  eggs,  from 
six  to  fifteen  in 
number,  are  laid 
in  cavities  in  the 
trunks  or  limbs  of 
trees.  The  wood- 
duck  is  one  of  our 
game-birds  that 
is  decreasing  so 
rapidly  in  num- 
bers that  it  seems 
on    the   verge   of 

extinction,  and  drastic  action  must  be  taken  by  the  federal  and 
state  governments  if  this  species  is  not  to  vanish  entirely. 

Order  15.  Falconiformes.  —  Falcon-like  Birds. — These 
diurnal  birds  of  prey  possess,  in  most  cases,  powerful  wings,  a 
stout,  hooked  bill  with  a  cere  at  the  base,  and  strong  toes  armed 
with  sharp  claws.  The  order  is  divided  into  the  Cathartid^, 
or  American  vultures,  the  GvPOGERANiDiE,  or  secretary-birds, 
the  Falconid^,  or  falcons,  and  the  Buteonid^e,  or  eagles, 
hawks,  kites,  etc. 


Fig.  492.  —  Wood-duck,  Aix  sponsa 


6o4 


COLLEGE  ZOOLOGY 


The  nine  or  ten  species  of  American  vultures  are  weaker  than 
the  other  Falconiformes.  They  live  on  carrion  and  are  valu- 
able in  warm  countries  as  scavengers.  The  species  occurring  in 
the  United  States  are  the  turkey-vulture  or  turkey-buzzard, 
Cathartes  aura,  the  black  vulture  or  carrion  crow,  Catharista 
urubu,    and   the    California  vulture,  Gymnogyps  californianus. 

The  California  vulture 
and  the  condor,  Sar- 
corhamphus  gryphus 
(Fig.  493),  which  lives 
in  the  Andes  Moun- 
tains, are  two  of  the 
largest  of  flying  birds. 
The  secretary-bird, 
Gypogeranus  secre- 
tarius,  of  South  Africa, 
is  the  only  represent- 
ative of  the  family 
Gypogeranid^.  Its 
common  name  was 
suggested  by  the  re- 
semblance of  some 
plumes  on  its  head  to 
a  bunch  of  quills  stuck 
Secretary-birds  feed  on  frogs,  toads. 


Fig.  493. 


Condor,  Sarcorhamphus  gryphus 
(From  Evans.) 


behind  the  ear  of  a  clerk, 
insects,  and  snakes. 

The  FALCONID.E  are  the  falcons,  tropical  goshawks,  and 
caracaras.  About  seventeen  species  of  the  genus  Falco  are 
found  in  North  America.  The  white  gyrfalcon,  F.  islandus, 
inhabits  the  Arctic  regions;  the  prairie-falcon,  F.  mexicanus, 
occurs  in  the  western  United  States;  the  duck-hawk,  F.  per- 
egrinus  anatum,  ranges  over  both  North  and  South  America; 
the  pigeon-hawk,  F.  columbarius  columbarius,  is  a  North  Ameri- 
can species;  and  the  sparrow-hawk,  F.  sparverius  sparverius  in- 
habits North  America  east  of  the  Rocky  Mountains.    All  of 


CLASS  AVES 


605 


Fig.    494.  —  Swainson's     hawk,      Buteo 
swainsoni.     (From  Fisher,  Yearbook  U.  S. 


L894.) 


these  birds  are  of  medium 

size  and  active.     The  wings 

are  long  and  pointed,  and 

the  bill  has  a  pronounced 

notch  and  tooth. 

The  two  species  of  cara- 

caras  that  reach  the  United  \  ' 

States  are  known  as  carrion- 
buzzards.     Audubon's  cara- 

cara,  Polyborus  cheriway,  is 

found  in  Florida.     It  lives 

largely  on  carrion,  but  also 

captures  frogs,  Hzards,  and 

snakes.  Dep't  Agric, 

The  BuTEONiD^  are  the 

kites,  buzzards,  eagles,  hawks,  ospreys.  Old-world  vultures,  and 

harriers.     Common  North  American  representatives  of   these 

groups  are  the  swallow- 
tailed  kite,  Elanoides  for- 
ficatus,  which  occurs  in  the 
warm  temperate  regions; 
the  osprey,  or  fish-hawk, 
Pandion  haliaetus  caro- 
linensis,  inhabiting  temper- 
ate and  tropical  America; 
the  bald  eagle,  Haliaetus 
leticocephalus,  generally  dis- 
tributed in  North  America; 
the  red-shouldered  hawk, 
Buteo  lineatus;  Swainson's 
hawk,  Buteo  swainsoni 
(Fig.  494)  ;  the  marsh- 
hawk,  or  harrier,  Circus 
Fig.    495  —Cooper's     hawk,    Accipiter     h^.^i^f.^:...  .     tVip    rpH  taileH 

coo  peri.       (From    Fisher,    Yearbook    U.   S.     f^^^^^omUS ,      tne    rea-tailed 

Dep't  Agric,  1894.)  hawk,   or  buzzard,    Buteo 


6o6  COLLEGE  ZOOLOGY 

horealis;  the  Cooper's  hawk,  Accipiter  cooperi  (Fig.  495);  and 
the  goshawk,  Astur  atricapillus. 

Order  16.  Galliformes.  —  Fowl-like  Birds.  —  This  is  a 
widely  distributed  group  containing  seven  famiHes,  only  two 
of  which  have  North  American  representatives:  (i)  the  Cra- 
ciDM  or  curassows  and  guans,  with  one  species  in  Texas ;  and 
(2)  the  PHASiANiDiE,  or  turkeys,  partridges,  etc. 

The  PHASiANiDiE  are  the  true  game-birds,  and  are  known  as 
bob-whites,  quail,  grouse,  partridges,  ptarmigan,  chickens,  hens, 
and  turkeys.  Among  the  best-known  species  inhabiting  the 
United  States  are  the  wild  turkey,  Meleagris  gallopavo  silvestris, 
which  is  the  largest  American  game-bird  and  a  native  species,  but 
now  nearly  extinct;  the  bob-white,  or  quail,  Colinus  virginianus ; 
the  ruffed  grouse,  Bonasa  umhellus ;  the  willow  ptarmigan, 
Lagopus  lagopus,  of  the  Arctic  regions;  and  the  prairie-chicken, 
Tympanuchus  americanus. 

The  game-birds  are,  as  a  rule^  terrestrial,  but  many  of  them 
roost  or  feed  in  trees.  Their  nests  are  usually  made  on  the 
ground  in  grass  or  leaves,  and  generally  a  large  number  of  eggs, 
from  six  to  eighteen,  are  laid.  The  members  of  one  family 
often  remain  together  as  a  "  covey,"  and  in  some  species  the 
coveys  unite  to  form  large  flocks. 

Order  17.  Gruiformes.  —  Crane -like  Birds. — The  seven 
families  belonging  to  this  order  contain  mostly  wading  birds 
with  incompletely  webbed  front  toes.  The  families  Rallidje 
and  GRUiDiE  are  represented  by  North  American  species. 

The  RALLID.E  are  the  rails,  gallinules,  and  coots.  The  rails 
are  seldom  seen,  spending  most  of  their  time  among  the  reeds  and 
rushes  in  marshes.  The  king-rail,  Rallus  elegans,  of  eastern 
North  America  is  a  large  species,  being  about  eighteen  inches 
in  length.  The  gallinules  also  inhabit  marshes.  The  Florida 
gallinule,  Gallinula  galeata,  is  a  common  form.  The  coots  are 
frequently  called  mud-hens,  and  sometimes  hell-divers,  because 
of  their  ability  to  dive  quickly.  There  is  only  one  common 
species,  Fulica  americana. 


CLASS  AVES 


607 


The  Gruid-'E  are  the  cranes/ courlans,  and  trumpeters.  The 
cranes  are  large  birds  with  long  legs  and  neck.  They  live  in 
grassy  plains  and  marshes.  The  whooping-crane,  Grus  ameri- 
cana,  measures  about  four  and  a  half  feet  in  length,  and  has  a 
spread  of  wings  of  about  eight  feet.  It  breeds  in  central  North 
America,  making  a  nest  of  grasses  knd  weed  stalks  on  marshy 
ground. 

Order  18.  Charadriiformes.  —  Plover-like  Birds.  —  Five  of 
the  twelve  families  in  this  order  have  North  American  repre- 


FlG.   496. 


Spotted  Sandpiper,  Aclitis  macularia.      (From  Davenport, 
after  Fuertes.) 


sentatives :  (i)  the  Charadriid^,  plovers,  snipes,  and  curlews; 
(2)  the  JACANID.E,  jacanas;  (3)  the  Larid^,  gulls,  terns,  and 
skimmers;  (4)  the  Alcid^,  auks;  and  (5)  the  Columbid.^, 
pigeons. 

The  CHARADRiiDiE  are  the  turnstones,  oyster-catchers,  lap- 
wings, true  plovers,  dotterels,  avocets,  stilts,  phalaropes,  sand- 
pipers, curlews,  whimbrels,  woodcock,  snipe,  and  dowitchers. 


6o8 


COLLEGE  ZOOLOGY 


The  spotted  sandpiper,  Actitis  macularia  (Fig.  496),  which  may 
be  taken  as  an  example  of  this  enormous  family,  occurs  through- 
out temperate  North  America.  It  lives  in  the  vicinity  of  water, 
and  feeds  upon  insects,  earthworms,  and  other  small  animals. 
The  four  eggs  are  laid  in  a  hollow  in  the  ground,  and  the  young 
are  able  to  run  about  as  soon  as  hatched. 

The  Jacanid^  are  tropical  marsh-birds,  with  very  long  toes 
and  claws  enabling  them  to  walk  over  lily  pads  without  sinking. 
The  Mexican  jacana,  Jacana  spinosa^  reaches  Texas. 


Fig.  497. 


Common  tern,  Sterna  hirundo. 
after  Fuertes.) 


(From  Davenport, 


The  LARiDiE  are  known  as  gulls,  terns,  skimmers,  kittiwakes, 
noddies,  skuas,  and  jaegers.  The  American  herring-gulls,  Larus 
argentatus,  are  about  two  feet  long.  They  breed  along  the 
Atlantic  coast  and  also  in  the  interior  from  Minnesota  north- 
wards. Their  nests  are  built  on  the  ground  of  grasses,  seaweed, 
etc.,  and  two  or  three  eggs  are  laid.  The  terns,  or  sea-swallows 
(Fig.  497) ,  are  as  a  rule  smaller  and  slimmer  than  the  gulls.  They 
frequent  the  shores  of  both  fresh  and  salt  water,  feed  upon  fish, 


CLASS  AVES 


609 


and  nest  in  colonies.  The  black  skimmer,  Rynchops  nigra,  is 
found  along  our  Atlantic  coast.  It  flies  along  the  surface  of  the 
water  with  its  lower  mandible  immersed,  and  literally  skims  small 
aquatic  animals  from  the  top. 

The  Alcid^  are  the  puffins,  auklets,  murrelets,  murres, 
guillemots,  and  true  auks.  They  spend  a  large  part  of  their 
existence  at  sea.  Most  of  them  are  strong  fliers,  and  excellent 
swimmers  and  divers,  but  very  awkward  on  land.  They  feed  on 
fish,  crustaceans,  and  other  small  marine  animals,  and  nest  in 
colonies,  usually  on  rocky  shores.  The  puffins,  or  sea-parrots, 
are  grotesque-looking  birds 
with  enormous  beaks  that  are 
grooved  and  brightly  colored. 
The  murres  possess  bills  which 
are  narrow  and  without 
grooves. 

The  true  auks  are  North 
American  birds  represented 
by  three  species.  The  great 
auk,  or  garefowl,  Plautus  im- 
pennis  (Fig.  498),  became  ex- 
tinct in  1844,  when  the  last 
one  appears  to  have  been 
killed.  They  were  destroyed 
for  their  feathers,  and  their  eggs  were  used  as  food.  "  All  that 
remains  to-day  of  the  Great  Auk  are  about  seventy  skins,  sixty- 
five  eggs,  and  some  twenty- five  more  or  less  perfect  but  com- 
posite skeletons,  that  is,  skeletons  made  up  from  the  bones  of 
many  different  individuals."     (Knowlton.) 

The  CoLUMBiD^  are  the  pigeons  or  doves  (Fig.  470)  of  which 
twelve  of  the  three  hundred  known  species  occur  in  North 
America.  The  passenger-pigeon,  Ectopistes  migratorius,  is  an- 
other bird  that  is  practically  extinct,  although  flocks  were  seen 
a  century  ago  that  contained  over  two  billion  birds.  The  mourn- 
ing-dove, Zenaidura  macroura,  is  common  and  often  mistaken 
2  R 


Fig.  498.  —  Great  auk,  Plautus  impennis. 
(From  Evans,  after  Hancock.) 


6io 


COLLEGE  ZOOLOGY 


for  the  passenger-pigeon.  It  makes  a  flimsy  nest  of  a  few  twigs, 
and  lays  two  white  eggs.  The  young  are  naked  when  born, 
and  are  fed  by  regurgitation. 

Order  19.  Cuculif ormes.  —  Cuckoo-like  Birds.  —  This  order 
contains  the  cuckoos,  plantain-eaters,  lories,  nestors,  cockatoos, 
and  parrots.  The  cuckoos  (Family  Cuculid^e)  are  mostly 
tropical  birds.  The  majority  of  them  do  not  build  a  nest,  but  lay 
their  eggs  in  the  nests  of  other  birds.  This  is  not  true,  however, 
of  the  North  American  species.  The  black-billed  and  yellow- 
billed  cuckoos  (Fig.  499)  of  this  country  are  long,  slender  birds 

of  solitary  habits  and  with 
the  peculiar  vocal  powers 
which  have  given  them 
their  common  name. 

The  American  species 
of  parrots,  about  one 
hundred  and  fifty  in 
number,  are  included  in 
the    family   PsixxACiDiE. 


Only 


one     species. 


the 


Fig.  499.  —  Yellow-billed  cuckoo,  Coccyzus 
americanus.  (From  Judd,  Bui.  17,  Bur. 
Biol.  Survey,  U.  Si  Dep't  Agric.) 


Carolina  paroquet,  Conu- 
ropsis  carolinensis,  occurs 
in  the  United  States. 
Parrots  and  paroquets  live  in  forests  and  feed  on  fruits  and 
seeds.  They  have  shrill  voices,  but  can,  with  few  exceptions,  be 
taught  to  talk.  The  African  parrot^  Psittacus  erythacus,  learns 
to  talk  most  readily. 

Order  20.  Coraciif ormes.  —  Roller-like  Birds.  — The  birds 
placed  in  this  order  may  be  grouped  into  seven  suborders,  and 
about  eighteen  families.  They  include  the  rollers,  motmots, 
kingfishes,  bee-eaters,  hornbills,  hoopoes,  oil-birds,  frogmouths, 
goatsuckers,  humming-birds,  swifts,  colies,  trogons,  puff-birds, 
jacamars,  barbets,  honey-guides,  toucans,  woodpeckers,  wry- 
necks, and  owls. 

There  are  about  two  hundred  species  and  subspecies  of  king- 


CLASS  AVES 


6ii 


fishers  (Alcedinid^)  ,  three  of  which  occur  in  North  America. 
The  belted  kingfisher,  Ceryle  alcyon  (Fig.  500),  breeds  from 
Florida  to  Labrador.  Its  five  to  eight  white  eggs  are  laid  at  the 
end  of  a  horizontal  hole  about  six  feet  deep  dug  by  the  birds 
usually  in  the  bank  of  a  stream.     The  kingfisher  captures  small 


Fig.  500.  —  Belted  kingfisher,  Ceryle  alcyon.     (From  Davenport, 
after  Fuertes.) 

fish  by  hovering  over  a  stream  and  then  plunging  into  the  water 
and  securing  the  unsuspecting  prey  in  its  bill. 

The  ow^ls  (Strigid.^)  are  the  nocturnal  birds  of  prey.  They 
possess  large,  rounded  heads,  strong  legs,  feet  armed  with  sharp 
claws,  strong  bills  with  the  upper  mandible  curved  downward, 
large  eyes  directed  forward  and  surrounded  by  a  radiating  disc 
of  feathers,  and  soft,  fluffy  plumage  which  renders  them  noiseless 


6l2 


COLLEGE  ZOOLOGY 


during  flight.  Owls  feed  upon  insects,  mice,  rats,  and  other 
small  mammals,  birds,  and  fish.  The  indigestible  parts  of  the 
food  are  cast  out  of  the  mouth  in  the  form  of  pellets.  Most 
species  are  beneficial  to  man. 

The  great  horned  owl,  Buho  virginianus  (Fig.  501),  is  one 
of  the  large  North  American  species.  It  nests  in  old  squirrels' 
and  hawks'  nests,  in  hollow  trees,  or  in  crevices  in  rocky 
cliffs.  Two  or  three  large  white  eggs  are  laid.  Its  food  con- 
sists principally  of  birds 
and  mammals,  especially 
rabbits,  and  its  harmful 
and  beneficial  qualities  are 
about  equal. 

The  goatsuckers  (Capri- 
MULGiD^)  are  represented 
in  North  America  by  thir- 
teen species,  of  which  the 
whippoorwill  and  night- 
hawk  are  the  best  known. 
The  whippoorwill,  Antrosto- 
mus  vociferus,  inhabits  the 
woods  and  thickets  of  east- 
ern North  America.  It 
is  most  active  after  sun- 
down and  early  in  the 
morning,  when  it  captures 
its  insect  food'  while  on  the  wing.  The  two  eggs  are  laid  on 
the  leaves  in  the  woods.  The  night-hawk,  Chordeiles  virginia- 
nus, has  a  range  similar  to  that  of  the  whippoorwill.  During 
the  day  it  perches  on  a  limb,  fence  post,  or  on  the  groimd, 
but  in  the  evening  it  mounts  into  the  air  after  its  insect  prey. 
The  two  eggs  are  laid  on  the  bare  ground,  usually  on  a  hillside 
or  in  an  open  field;  often  they  are  deposited  on  the  gravel  roofs 
of  city  buildings. 
.   The  humming-birds  (TROCHiLiDiE),  which  are  confined  to  the 


Fig.  501.  —  Great-horned  owl,  Bubo  vir- 
ginianus. (From  Fisher,  Yearbook  U.  S. 
Dep't  Agric,  1894.) 


CLASS  AVES 


613 


New  World,  have  been  appropriately  called  feathered  gems,  or, 
according  to  Audubon,  "  glittering  fragments  of  the  rainbow." 
Only  seventeen  of  the  five  hundred  or  more  species  occur  in  the 
United  States,  and  only  one,  the  ruby-throated  humming-bird, 
Trochilus  colubris  (Fig.  502),  is  found  east  of  the  Mississippi 
River.  This  beautiful  little  bird  is  only  three  and  three-quarters 
inches  in  length.  It  hovers  before  flowers,  from  which  it  obtains 
nectar,  small  insects,  and 
spiders.  The  nest,'which 
is  saddled  on  the  limb  of 
a  tree,  is  made  of  plant 
down  and  so  covered  with 
lichens  as  to  resemble  its 
surroundings  very  closely. 
Two  tiny  white  eggs  are 
laid.  The  young  are  fed 
by  regurgitation. 

The  swifts  (Micro- 
PODiD^)  resemble  the 
swallows  superficially,  but 
their  anatomy  shows  that 
there  is  no  real  resem- 
blance between  the  two 
groups.  Of  the  one  hun- 
dred species  and  sub- 
species of  swifts,  four  are 

inhabitants  of  North  America,  and  one,  the  chimney-swift 
(Chcetura  pelagica),  breeds  commonly  in  eastern  North  America. 
This  species  formerly  made  its  nest  in  hollow  trees,  but  now 
usually  frequents  chimneys.  When  in  the  open  air  it  is 
always  on  the  wing,  catching  insects  or  gathering  twigs  from 
the  dead  branches  of  trees  for  its  nest.  The  twigs  are  glued 
together  with  saliva  and  firmly  fastened  to  the  inside  of  the 
chimney,  forming  a  cup-shaped  nest.  Certain  species  of  swifts 
inhabiting  China  make  nests  entirely  of  a  secretion  from  the 


Fig.  502.  —  Ruby-throated  humming-bird, 
Trochilus  colubris.  (From  Davenport,  after 
Fuertes.) 


6i4 


COLLEGE  ZOOLOGY 


salivary    glands,    producing    the    edible    birds'-nests    of    the 
Chinese. 

The  woodpeckers  (Picid^),  comprising  about  three  hundred 
and  fifty  species,  are  found  in  wooded  regions  almost  everywhere 
except  in  the  Australian  region  and  Madagascar.  About  fifty 
species  occur  in  North  America.  The  downy,  hairy,  and  red- 
headed woodpeckers,  the  flicker,  and  the  yellow-bellied  sap- 
sucker  are  the  best  known.    Woodpeckers  use  their  chisel-shaped 

bills  for  excavating  holes 
in  trees,  at  the  bottom  of 
which  their  eggs  are  laid, 
or  for  digging  out  grubs 
from  beneath  the  bark. 
Most  of  them  are  of  great 
benefit  because  of  the 
insects  they  destroy,  but 
the  yellow-bellied  sap- 
sucker  (Fig.  503)  is  harm- 
ful, since  it  eats  the  cam- 
bium of  trees  and  sucks 
sap. 

Order  21.  Passeri- 
formes.  —  Sparrow-like 
Birds  (Fig.  504).  — It  is 
necessary,  because  of  lack 
of  space,  to  refer  the 
student  to  books  on  birds  for  a  detailed  account  of  the  birds 
included  in  this  order.  On  page  591  will  be  found  a  list  of 
the  principal  families.  Almost  half,  about  seven  thousand 
species  and  subspecies,  of  all  the  birds  known  belong  to  this 
order.  They  are  grouped  into  sixty-four  families ;  rep- 
resentatives belonging  to  twenty- five  of  these  occur  in  North 
America. 

Passerine  birds  are  usually  small  or  of  medium  size,  but  are 
the  most  highly  organized  of  the  class  Aves.     Their  feet  are 


Fig.  503. — Yellow-bellied  sapsucker,  Sphy- 
rapicus  varius.  (From  Judd,  Bui.  17,  Bur. 
Biol.  Survey,  U.  S.  Dep't  Agric.) 


CLASS  AVES 


6lS 


Fig.  504.  — ^  Types  of  common  passerine  birds.  (From  Judd,  Bui.  17,  Bur. 
Biol.  Survey,  U.  S.  Dep't  Agric.)  A,  kingbird,  Tyrannus  tyrannus  (Tyran- 
NiD^).  B,  blue  jay,  CyanociUa  crislata  (Corvid.^).  C,  bobolink,  Dolichonyx 
oryzivorus  (Icterid^).  D,  song-sparrow,  Melospiza  melodia  (Fringillid^). 
E,  barn-swallow,  Hirundo  erythrogastra  (Hirundinid^).  F,  cedar  waxwing, 
Bombycilla  cedrorum  (Bombycillidae).  G,  house  wren.  Troglodytes  aedon 
(Troglodytid.^).     H,  mocking-bird,   Mimus  polygloUus  (Mimid^). 


6l6  COLLEGE  ZOOLOGY 

four-toed  and  adapted  for  grasping.  The  first  toe,  or  hallux, 
is  directed  backward,  and  is  on  a  level  with  the  other  three,  which 
are  directed  forward. 

Two  superfamilies  of  the  Passeriformes  have  North  Amer- 
ican representatives,  the  Clamatores  and  the  Oscines.  The 
Clamatores  are  non-melodious  birds,  with  a  syrinx  which  is  in- 
effective as  a  musical  apparatus.  Only  two  families  occur  in 
this  country:  (i)  the  CoxiNGiDiE  or  chatterers,  with  one  species 
recorded  from  Arizona;  and  (2)  the  Tyrannid^e,  or  tyrant  fly- 
catchers, with  a  large  number  of  common  species,  such  as  the 
kingbird,  phoebe,  and  wood-pewee. 

The  Oscines  are  the  singing  birds.  Twenty- five  of  the  forty- 
nine  families  are  known  from  North  America.  Many  of  the 
"  singing-birds  "  are  almost  voiceless,  but  their  structure  neces- 
sitates their  inclusion  in  the  superfamily. 

4.  A  General  Account  of  the  Class  Ayes 

a.  Form  and  Function 

The  bodies  of  birds  have  become  adapted  to  various  environ- 
ments. This  adaptation  is  best  shown  by  the  wings,  tails,  feet, 
and  bills. 

Wings.  ■ —  The  wings  of  most  birds  are  used  as  organs  of  flight, 
and  the  more  time  spent  in  the  air,  the  longer  and  stronger  they 
become.  Birds  like  the  swallows,  gulls,  and  albatrosses  have 
long,  pointed  wings  characteristic  of  aerial  birds;  whereas  ter- 
restrial birds,  such  as  the  bob-white  and  song-sparrow,  possess 
short,  rounded  wings  which  enable  them  to  fly  rapidly  for  short 
distances.  Many  species  of  birds  that  spend  their  lives  mostly 
in  the  water  possess  wings,  but  are  unable  to  fly.  For  example, 
the  wings  of  the  penguins  (Fig.  486)  are  like  flippers  and  covered 
with  scale-like  feathers;  they  are  moved  alternately  and  are  the 
sole  organs  of  locomotion  in  swimming  under  water,  the  legs 
being  used  simply  as  a  rudder.     Other  sea-birds,  like  the  auks 


CLASS  AVES 


617 


and  murres  (Alcid^e),  use  their  wings  effectively  in  diving  be- 
neath the  waves. 

Among  the  flightless  birds  belong  a  number  of  terrestrial 
species,  like  the  ostrich  (Fig.  480),  rhea  (Fig.  481),  emeu  (Fig.  482), 
and  kiwi  (Fig.  485).  These  birds  all  possess  the  remnants  of 
wings,  but  these  are,  for  the  most  part,  of  no  use  in  locomotion, 
and  in  some  (Fig.  485)  are  practically  concealed  beneath  the 


flfei 


Fig.  505. 


A,  lyre-bird,  Menura  superba.     (From  Evans.)     B,  bird  of 
paradise,  Paradisea  rubra.     (From  Brehm.) 


feathers.  Their  legs  are,  on  the  other  hand,  very  well  developed, 
and  quickly  carry  them  out  of  danger. 

The  primitive  use  of  wings  was  for  climbing.  ArchcBopteryx 
(Fig.  477)  was  provided  with  three  strong  claws  on  its  fore  limbs. 
Of  living  birds  the  young  of  the  hoactzin,  a  peculiar  bird  inhabit- 
ing South  America,  should  be  mentioned,  since  it  is  able  to  climb 
about  before  it  can  fly,  by  the  aid  of  two  claws  on  each  fore 
limb. 

Wings  may  also  serve  as  organs  of  offense  and  defense,  or  as 
musical  instruments;  for  example,  the  "  drumming  "  of  the  ruffed 
grouse. 

Tails.  —  During  flight  the  tail  acts  as  an  aerial  rudder,  and 
a  long-tailed  bird  is  able  to  fly  in  short  curves,  or  follow  an 


6i8  COLLEGE  ZOOLOGY 

erratic  course  without  difficulty.  The  tail  is  light,  and  therefore 
easy  to  manage,  and  the  tail-feathers  {rectrices,  Fig.  471,  RX) 
are  firmly  supported  by  the  terminal  bone  of  fused  vertebrae, 
the  pygostyle  (Fig.  471,  Q).  Movement  of  the  tail  is  allowed 
by  the  freely  movable  vertebrae  just  preceding  the  pygostyle. 
While  perching  the  tail  acts  as  a  "  balancer."  Birds  that  cUng 
to  the  sides  of  trees,  like  the  woodpeckers  (Fig.  503),  or  to  the 
sides  of  other  objects,  like  the  chimney-swift,  brace  themselves 
by  means  of  their  tails. 

In  many  birds  the  tail  of  the  male  differs  from  that  of  the 
female,  being  more  beautiful  in  the  former,  and  serving  as  a 
sexual  character.  Two  of  the  most  famous  of  these  dimorphic 
species  are  the  lyre-bird  (Fig.  505,  A)  and  the  birds  of  paradise 
(Fig.  505,  B). 

Feet.  —  The  feet  (Fig.  506)  are  used  for  locomotion,  for  ob- 
taining food,  for  building  nests,  and  for  offensive  and  defensive 
purposes.  Ground-birds  usually  have  strong  feet,  fitted  for 
running  (Fig.  506,  h)^  or  scratching  (c);  perching  birds  (see  p. 
616)  possess  feet  adapted  for  grasping  a  perch  (d);  aerial  birds 
use  their  feet  very  little,  and  these  organs  are  consequently  weak 
(a,  e) ;  swimming  birds  (^,  I,  n)  and  wading  birds  (g,  k,  m)  are 
provided  with  toes  that  are  more  or  less  completely  lobed;  birds 
of  prey  possess  strong  feet  with  sharp  claws  (/)  for  capturing 
other  animals;  woodpeckers  have  feet  {b)  adapted  for  clinging 
to  the  bark  of  trees. 

Bills.  —  The  bills  of  birds  (Fig.  507)  serve  as  hands,  and  their 
most  important  function  is  to  procure  food.  Since  bills  are  also 
used  to  construct  nests,  to  preen  feathers,  and  to  perform  other 
duties,  their  adaptations  are  such  as  to  make  them  serve  several 
purposes.  In  preening  the  feathers  a  drop  of  oil  is  pressed  from 
the  oil-gland  at  the  base  of  the  tail  and'  spread  by  means  of  the 
bill. 

Seed-eating  birds  possess  short,  strong  bills  for  crushing  seeds 
(Fig.  507,  c) ;  birds  that  eat  insects  have  longer  and  weaker  bills 
{dy  q);   birds  of  prey  are  provided  with  strong,  curved  beaks 


CLASS  AVES 


619 


fitted  for  tearing  flesh  (e);  the  pelicans  (g)  and  skimmers  (i) 
scoop  up  fishes  and  other  animals  from  the  water;  and  the  avocet 
(h)  uses  its  long,  cun^ed  bill  like  a  scythe,  swinging  it  from  side 


Fig.  S06.  —  The  most  important  forms  of  birds'  feet,  o,  cKnging  foot  of 
a  swift,  Cypseliis  ;  h,  climbing  foot  of  woodpecker,  Picus ;  c,  scratching  foot 
of  pheasant,  Phasianus ;  d,  perching  foot  of  ouzel,  Turdus ;  e,  foot  of  king- 
fisher, Alcedo;  f,  seizing  foot  of  falcon,  Falco;  g,  wading  foot  of  stork,  Myc- 
teria;  h,  running  foot  of  ostrich,  Struthio;  i,  swimming  foot  of  duck,  Mergus; 
k,  wading  foot  of  avocet,  Recurvirostra;  I,  diving  foot  of  grebe,  Podicepes; 
m,  wading  foot  of  coot,  Fulica;  n,  swimming  foot  of  tropic-bird,  Phaeton. 
(From  Sedgwick's  Zoology:   b,  c,  d,  f,  n,  from  regne  animal.) 


620 


COLLEGE  ZOOLOGY 


to  side  near  the  bottom  in  shallow  water  and  securing  food  it 
cannot  see;   the  bill  of  the  woodpecker  serves  as  a  chisel;   and 


Fig.  507.  —  The  most  important  forms  of  birds'  beaks,  a,  flamingo,  Phoe- 
nicopterus;  b,  spoonbill,  Platalea;  c,  yellow  bunting,  Emberiza;  d,  thrush, 
Turdus;  e,  falcon,  Falco;  J,  duck,  Mergus;  g,  pelican,  Pelicanus;  h,  avocet, 
Recurvirostra;  i,  black  skimmer,  Rhynchops;  k,  pigeon,  Columba;  I,  shoebill, 
Baloeniceps;  m,  stork,  Anastomus;  n,  aracari,  Pleroglossus;  0,  stork,  Mycteria; 
P,  bird  of  paradise,  Falcinellus;  q,  swift,  Cypselus.  (From  Sedgwick's  Zoology; 
a,  b,  c,  d,  k,  after  Naumann;  g,  i,  m,  o,  after  regne  animal;  1,  after  Brehm.) 

that  of  the  woodcock  as  a  probe  for  capturing  small  animals 
in  the  muddy  shores  of  ponds  and  streams.  Many  other  ex- 
amples might  be  cited. 


CLASS   AVES  621 

h.  The  Colors  of  Birds 

Birds  are  among  the  most  beautifully  colored  of  all  animals. 
This  color  is  due  to  pigments  within  the  feathers  (chemical 
colors)  or  to  structural  peculiarities,  such  as  prismatic  shapes 
which  break  up  the  rays  of  light  into  their  component  colors 
(physical  colors),  or  to  both  causes.  Nestling  birds  possess  dis- 
tinctively colored  feathers  which  later  give  way  to  the  "  imma- 
ture plumage  ";  this  is  worn  usually  throughout  the  first  winter, 
and  is  generally  dull  in  color,  often  resembUng  the  plumage  of 
the  adult  female.  Males  and  females  frequently  differ  in  color 
(sexual  dimorphism) ,  especially  during  the  breeding  season,  when 
the  male  acquires  a  brightly  colored  coat.  The  attempt  to  ex- 
plain this  difference  has  led  to  the  theory  of  sexual  selection.^ 

One  important  use  of  color  is  its  protective  value  to  the  bird. 
The  colors  and  color  patterns  of  birds,  as  well  as  other  animals, 
are  such  as  to  conceal  these  animals  amid  their  surroundings.^ 

c.  Bird  Songs 

The  songs  of  birds,  as  explained  on  page  585,  are  produced 
by  the  air  passing  through  the  syrinx.  For  one  who  wishes  to 
study  birds,  a  knowledge  of  bird  songs  is  indispensable,  since  one 
hears  a  great  many  more  birds  than  he  is  able  to  see.  Songs 
should  be  distinguished  from  call-notes.  The  former  are  usually 
heard  during  the  breeding  season,  and  are  generally  limited  to 
the  males.  Call-notes,  on  the  other  hand,  are  uttered  throughout 
the  year,  and  correspond  in  their  meaning  and  effect  to  our  con- 
versation. By  means  of  call-notes  a  bird  is  able  to  express  anxi- 
ety or  fear,  and  to  communicate  to  a  limited  extent  with  other 
birds. 

d.  Bird  Flight 

One  of  the  most  important  functions  of  birds  is  that  of  flight. 
The  bodies  of  flying  birds  are  structurally  adapted  so  as  to  offer 

1  Darwin,  The  Descent  of  Man  and  Selection  in  Relation  to  Sex. 

2  Thayer,  Concealing  Coloration  in  the  Animal  Kingdom. 


622  COLLEGE  ZOOLOGY 

little  resistance  to  the  air;  the  wings  are  placed  high  up  on  the 
trunk  to  prevent  the  body  from  turning  over;  and  the  bones  are 
hollow  and  the  body  contains  air-sacs,  which  decrease  the  specific 
gravity. 

In  flying,  the  tip  of  the  wing  describes  a  figure  8  as  it  is  brought 
downward  and  forward  and  then  backward  and  upward  (Fig. 
508).  The  wing  v/orks  on  the  principle  of  the  inclined  plane, 
and  both  the  down  and  up  strokes  propel  the  bird  forward.  The 
body  is  sustained  in  the  air  by  the  downward  strokes,  which  force 
it  upward. 

A  great  many  birds  are  able  to  glide,  and  a  number  are  fond 
of  sailing  or  soaring.  Birds  are  able  to  glide  or  skim  by  spread- 
ing their  wings  and  then  moving  forward  by  means  of  their  ac- 


FiG.  508.  —  Gull  flying.     (From  Headley,  after  Marey.) 

quired  velocity.     In  soaring,  birds  do  not  depend  upon  acquired 
velocity,  but  apparently  rely  upon  favorable  air  currents. 

The  rate  of  speed  at  which  birds  fly  varies  considerably.  .  The 
carrier-pigeon  in  this  country  maintains  an  average  racing  speed 
of  about  thirty- five  miles  per  hour.  Ninety  miles  per  hour  has 
been  recorded  for  ducks  (Forrester),  but  this  rate  is  not  sustained 
for  any  great  length  of  time.  During  long  flights  the  distances 
traveled  per  day  are  comparatively  short,  e.g.  an  albatross  is 
known  to  have  covered  over  three  thousand  miles  in  twelve  days 
or  two  hundred  and  fifty  miles  per  day,  and  a  carrier-pigeon 
flying  from  Pensacola,  Florida,  to  Fall  River,  Massachusetts,  a 
distance  of  over  a  thousand  miles,  attained  a  daily  average  of 
seventy-six  miles. 

e.   Bird  Migration 

Formerly  birds  were  supposed  to  hibernate  during  the  winter 
in  caves,  hollow  trees,  or,  in  the  case  of  swallows,  in  the  mud  at 


CLASS  AVES  623 

the  bottom  of  lakes  and  ponds.  This  is  now  known  to  be  incor- 
rect, and  when  birds  disappear  in  the  fall  they  depart  to  spend 
the  winter  in  a  more  congenial  southern  climate. 

Migration  means  moving  from  bne  place  to  another,  and  the 
idea  of  distance  is  emphasized.  Birds  are  the  most  famous  of 
all  animals  from  the  standpoint  of  their  migrations.  As  winter 
approaches  in  the  north  temperate  zone,  they  gather  together 
in  flocks  and  move  southward,  returning  on  the  advent  of  the 
following  spring.  Birds  that  breed  farther  north  spend  the 
winter  in  parts  of  the  temperate  zone. 

Not  all  birds  migrate,  for  example,  the  great  horned  owl  and 
bob- white  remain  with  us  throughout  the  winter.  Certain  other 
birds  move  southward  only  when  the  weather  becomes  very 
severe. 

One  of  the  most  remarkable  of  all  migratory  birds  is  the  golden 
plover.  These  plovers  arrive  in  the  "  barren  grounds  "  above 
the  Arctic  Circle  the  first  week  in  June.  In  August  they  fly 
to  Labrador,  where  they  feast  on  the  crowberry  and  become  very 
fat.  After  a  few  weeks,  they  reach  the  coast  of  Nova  Scotia,  and 
then  set  out  for  South  America  over  twenty-four  hundred  miles 
of  ocean.  They  may  or  may  not  visit  the  Bermuda  Islands  and 
the  West  Indies.  After  a  rest  of  three  or  four  weeks  in  the  West 
Indies  or  northern  South  America,  the  birds  depart  and  are  next 
heard  from  on  their  arrival  in  southern  Brazil  and  Argentine. 
Here  they  spend  the  summer,  from  September  to  March,  and  then 
disappear.  Apparently  they  fly  over  northern  South  America, 
and  Central  America,  and  over  the  central  portion  of  North 
America,  reaching  their  breeding  grounds  in  the  Arctic  Circle 
the  first  week  in  June.  The  elliptical  course  they  follow  is  ap- 
proximately twenty  thousand  miles  in  length,  and  this  remark- 
able journey  is  undertaken  every  year  for  the  sake  of  spending 
ten  weeks  in  the  bleak,  treeless,  frozen  wastes  of  the  Arctic 
Region. 

Most  birds  migrate  on  clear  nights  at  an  altitude  sometimes  of 
a  mile  or  more.     Each  species  has  a  more  or  less  definite  time  of 


624  COLLEGE  ZOOLOGY 

migration,  and  one  can  predict  with  some  degree  of  accuracy  the 
date  when  it  will  arrive  in  a  given  locality.  The  speed  of  migra- 
tion is,  as  a  rule,  rather  slow,  and  a  daily  rate  of  twenty-five 
miles  is  about  the  average. 

During  their  migrations,  birds  are  often  killed  in  great  num- 
bers by  striking  against  objects,  such  as  the  Washington  Monu- 
ment, lighthouses,  and  telegraph  wires.  Over  fifteen  hundred 
birds  were  killed  in  one  night  by  dashing  against  the  Bartholdi 
Statue  in  New  York  Harbor.  Birds  may  also  be  driven  out  to 
sea  or  be  killed  by  severe  storms. 

Many  theories  have  been  advanced  to  account  for  the  migra- 
tion of  birds,  such  as  the  temperature  and  condition  of  the  food 
supply.  Other  theories  attempt  to  explain  how  birds  find  their 
way  during  migration.  The  best  of  these  seems  to  be  the  "  fol- 
low-the-leader  "  theory.  According  to  this,  birds  that  have 
once  been  over  the  course  find  their  way  by  means  of  landmarks 
and  the  inexperienced  birds  follow  these  leaders. 

/.   The  Nests,  Eggs,  and    Young  of  Birds 

Some  birds,  like  the  hawks  and  owls,  mate  for  life,  but  the  ma- 
jority of  them  live  together  for  a  single  season  only.  The  nesting 
period  varies  according  to  the  species.  The  eggs  of  the  great 
horned  owl  are  often  deposited  before  the  snow  has  left  the 
ground,  but  most  birds  are  forced  to  wait  until  April  or  later, 
when  the  supply  of  insects  is  sufficient  to  feed  their  young. 

The  nest  site  is  chosen  with  considerable  care,  and  is  deter- 
mined upon  from  the  standpoint  of  protection.  As  a  rule,  birds 
conceal  their  nests,  or  else  build  them  in  places  that  are  prac- 
tically inaccessible;  for  example,  the  nest  of  the  song  sparrow 
is  hidden  beneath  a  tuft  of  grass,  whereas  that  of  the  great  blue- 
heron  is  placed  in  the  top  of  the  tallest  tree. 

Many  species,  like  the  auk  and  certain  other  sea-birds,  and  the 
night-hawk  and  whippoorwill,  make  no  pretence  to  build  a  nest, 
but  lay  their  one  or  more  eggs  directly  upon  the  ground.  The 
killdeer  and  other  plovers  deposit  their  eggs  in  a  small,  crudely 


CLASS  AVES  625 

lined  hollow  in  the  ground.  The  great  horned  owl  lays  its  eggs 
in  an  old  hawk's  or  squirrel's  nest.  The  mourning-dove  builds 
a  loose  platform  of  twigs.  Ther^  are  all  stages  of  complexity 
between  this  simple  attempt  and  the  beautifully  woven,  hanging 
nest  of  the  Baltimore  oriole.  Certain  features  distinguish  the 
nest  of  one  bird  from  that  of  another;  thus  the  nest  of  the  chip- 
ping sparrow  almost  invariably  contains  a  lining  of  horsehair, 
that  of  the  shrike  contains  feathers,  that  of  the  American  gold- 
finch is  lined  with  thistle-down,  and  the  nests  of  the  ruby- 
throated  humming-bird  and  the  wood  pewee  are  covered  exter- 
nally with  lichens. 

A  few  birds  not  only  do  not  build  nests,  but  even  refuse  to 
incubate  their  eggs  and  take  care  of  their  offspring.  This  is 
true  of  the  European  cuckoo  and  the  American  cow-bird.  The 
breeding  habits  of  the  latter  are  very  interesting.  There  are 
more  male  cowbirds  than  females  and  each  female  therefore  mates 
with  several  males,  —  a  condition  known  as  polyandry.  The 
females  seek  out  the  nests  of  other  birds,  usually  those  smaller 
than  themselves,  in  which  to  lay  their  eggs.  The  young  cow- 
birds  are  carefully  reared  by  their  foster  parents,  and  often  starve 
out  the  rightful  owners. 

The  eggs  of  birds  vary  in  size,  color,  and  number.  The  small- 
est eggs  are  those  of  certain  humming-birds,  measuring  less  than 
half  an  inch  long;  the  largest  eggs  are  those  of  the  extinct  ele- 
phant-birds of  Madagascar,  Mpyornis,  which  measure  over  thir- 
teen inches  in  length  (see  p.  598). 

As  a  rule,  eggs  laid  in  dark  places,  such  as  those  of  the  bank- 
swallow,  kingfisher,  woodpecker,  and  owl,  are  white.  Many 
eggs  are  colored,  some  possessing  a  uniform  ground  color;  others, 
spots  of  various  hues;  and  still  others,  both  a  ground  color  and 
spots.  These  colors  usually  vary  but  slightly  in  the  eggs  laid 
by  different  individuals  of  the  same  species,  and  those  of  one 
species  are,  in  most  cases,  easily  distinguished  from  those  of  an- 
other species. 

The  eggs  laid  at  a  setting  vary  in  number  from  one  to  about 


626  COLLEGE   ZOOLOGY 

twenty.  For  example,  the  murre  lays  one;  the  mourning  dove, 
two;  the  red- tailed  hawk,  two  or  three;  the  robin,  three  or  four; 
the  blue  jay  four  or  five;  the  bank  swallow,  six;  the  flicker,  six 
to  eight;  the  ruff ed  grouse,  eight  to  fourteen ;  the  bob-white,  ten 
to  eighteen. 

The  average  period  of  incubation  for  passerine  birds  is  about 
twelve  days.  The  eggs  of  the  ostrich  hatch  in  about  forty- five 
days.  In  some  cases  the  female  alone  incubates;  in  other  cases 
both  male  and  female  assist  in  incubation;  and  in  a  few  birds, 
such  as  the  ostrich,  the  male  performs  practically  all  of  this  duty. 

Two  general  classes  of  young  are  recognized:  (i)  those  that 
are  able  to  run  about,  like  young  chickens,  soon  after  hatching, 
known  as  precocious  birds;  and  (2)  those  that  remain  in  the  nest 
for  a  greater  or  less  period  before  they  are  able  to  take  care  of 
themselves.     The  latter  are  known  as  altricial  birds. 

g.  The  Economic  Importance  of  Birds 

Commercial  Value.  —  Without  taking  into  consideration  the 
more  than  three  million  dollars  annually  derived  from  poultry 
products  in  this  country,  we  may  say  that  the  principal  sources 
of  revenue  derived  from  birds  are  the  flesh  of  game  birds,  the 
eggs  of  certain  colonial  sea-birds,  the  feathers  of  many  species 
of  use  for  millinery  purposes,  and  the  excreta  and  ejecta  of  certain 
species,  which  have  accumulated  on  tropical  islands  and  are 
known  as  guano. 

Guano  contains  two  important  elements  of  use  in  fertilizing 
the  soil,  phosphoric  acid  and  nitrogen.  The  Chincha  Islands  off 
the  coast  of  Peru  have  been  for  centuries  the  habitation  of  large 
numbers  of  sea-birds,  whose  excreta  and  remains  have  dried  and 
formed  a  deposit  in  some  places  a  hundred  feet  thick.  The  sup- 
ply on  these  islands  is  now  almost  exhausted,  though  in  1853 
the  Peruvian  government  estimated  the  amount  at  that  time  at 
12,376,100  tons.  There  are  many  other  deposits  in  the  rainless 
latitudes  of  the  Pacific,  but  none  as  rich  as  were  those  of  the 
Chinchas. 


CLASS  AVES  627 

Birds  are  in  sdme  localities  persecuted  to  a  considerable  extent 
for  their  eggs,  which  are  used  as  food.  This  is  true  of  certain 
gulls,  terns,  herons,  murres,  and  ducks.  Egging  is  not  carried 
on  now  as  much  as  formerly,  since  many  of  the  colonies  have 
been  driven  away  from  their  breeding  places,  or  the  government 
has  prohibited  the  practice.  In  1854  more  than  five  hundred 
thousand  murres'  eggs  were  collected  on  the  Farallone  Islands 
and  sold  in  the  markets  of  San  Francisco  in  two  months. 

The  game-birds  have  been  and  still  are  in  certain  localities  a 
common  article  of  food.  Most  of  them,  however,  have  been  so 
persistently  hunted  by  sportsmen  and  market  men  that  they 
are  now  of  no  great  commercial  importance.  Several  species, 
like  the  wood-duck  and  heath-hen,  have  been  brought  to  the  verge 
of  extinction.  The  repeating  shotgun,  introduction  of  cold- 
storage  methods,  and  easy  transportation  facilities  soon  depleted 
the  vast  flocks  of  prairie-chickens  and  other  game-birds  of  the 
Middle  West.  One  New  York  dealer  in  1864  received  twenty 
tons  of  these  birds  in  one  consignment.  The  hunting  and  trans- 
portation of  game-birds  is  now  regulated  by  law  in  most  localities. 

The  use  of  birds'  skins  and  feathers  as  ornaments  has  been  for 
many  years  a  source  of  income  for  many  hunters,  middlemen,  and 
milliners.  Laws  and  public  sentiment  are  slowly  overcoming 
the  barbarous  custom  of  killing  birds  for  their  plumes,  and  it  is 
hoped  that  the  women  of  the  country  will  soon  cease  to  demand 
hats  trimmed  with  the  remains  of  birds. 

The  Value  of  Birds  as  Destroyers  of  Injurious  Animals.  — 
Within  the  past  two  decades  detailed  investigations  have  been 
carried  on  by  the  United  States  Department  of  Agriculture,  state 
governments,  and  private  parties  in  order  to  learn  the  relations 
of  birds  to  man  with  regard  to  the  destruction  of  injurious  ani- 
mals. The  results  of  these  researches  may  be  found  in  govern- 
ment publications  or  in  books  such  as  Weed  and  Dearborn's 
Birds  in  their  Relation  to  Man,  and  Forbush's  Useful  Birds  and 
their  Protection. 

A  very  large  proportion  of  the  food  of  birds  consists  of  insects. 


628 


COLLEGE  ZOOLOGY 


Figure  509  shows  diagrammatically  the  food  of  nestling  and 
adult  house  wrens,  birds  that  are  very  common  about  gardens. 
Practically  all  of  the  insects  devoured  by  birds  are  injurious  to 
plants  or  animals  and  consequently  harmful  to  man. 

Another  large  element  in  the  food  of  birds  consists  of  small 
mammals,  such  as  field-mice,  ground-squirrels,  and  rabbits. 
For  many  years  hawks,  owls,  and  other  birds  of  prey  have  been 
killed  whenever  possible,  because  they  were  supposed  to  be  in- 
jurious on  account  of  the  poultry  and  game-birds  they  captured. 


Fig.  509.  —  Diagram  showing  the  kind  and  comparative  quantity  of '  food 
of  the  nestling  (A)  and  adult  (B)  house  wren.  (From  Judd,  Bui.  17,  Bur.  Biol. 
Survey,  U.  S.  Dep't  Agric.) 


Careful  investigations  by  Dr.  A..  K.  Fisher  have  shown,  however, 
that  at  least  six  species  are  entirely  beneficial;  that  the  majority 
(over  thirty  species)  are  chiefly  beneficial;  that  seven  species 
are  as  beneficial  as  they  are  harmful;  and  that  only  the  gyrfal- 
cons,  duck-hawk,  sharp-shinned  hawk.  Cooper's  hawk  (Fig.  495), 
and  goshawk  are  harmful. 

As  examples  of  beneficial  birds  of  prey  may  be  mentioned 
(i)  the  rough-leg  hawk,  which  feeds  almost  entirely  on  meadow 
mice  during  its  six  nionths'  sojourn  in  the  United  States,  (2)  the 
red- tailed  hawk,  or  "  hen  hawk,"  sixty-six  per  cent  of  whose 
food  consists  of  injurious  mammals  and  only  seven  per  cent  of 


CLASS  AVES  629 

poultry,  and  (3)  the  golden  eagle,  which  is  highly  beneficial  in 
certain  localities  because  of  the  noxious  rodents  it  destroys. 
The  Cooper's  hawk  (Fig.  495)  is  the  real  "  chicken  hawk  ";  its 
food  is  made  up  largely  of  poultry,  pigeons,  and  wild  birds,  but 
also  includes  the  harmful  English  sparrows. 

The  beneficial  qualities  of  birds  are  well  shown  by  Dr.  S.  D. 
Judd  ^  from  a  seven  years'  study  of  conditions  on  a  small  farm 
near  Marshall  Hall,  Maryland.  Modern  methods  of  investiga- 
tion led  Dr.  Judd  to  the  following  conclusions:  — 

"  At  Marshall  Hall  the  English  sparrow,  the  sharp-shinned 
and  Cooper  hawks,  and  the  great  horned  owl  are,  as  everywhere, 
inimical  to  the  farmers'  interests  and  should  be  killed  at  every 
opportunity.  The  sapsucker  punctures  orchard  trees  exten- 
sively and  should  be  shot.  The  study  of  the  crow  is  imfavorable 
in  results  so  far  as  these  particular  farms  are  concerned,  partly 
because  of  special  conditions.  Its  work  in  removing  carrion 
and  destroying  insects  is  serviceable,  but  it  does  so  much  damage 
to  game,  poultry,  fruit,  and  grain  that  it  more  than  counter- 
balances this  good  and  should  be  reduced  in  numbers.  The  crow 
blackbird  appears  to  be  purely  beneficial  to  these  farms  during 
the  breeding  season  and  feeds  extensively  on  weed  seed  during 
migration,  but  at  the  latter  time  it  is  very  injurious  to  grain. 
More  detailed  observations  are  necessary  to  determine  its  proper 
status  at  Marshall  Hall. 

"  The  remaining  species  probably  do  more  good  than  harm,  and 
except  under  unusual  conditions  should  receive  encouragement 
by  the  owners  of  the  farms.  Certain  species,  such  as  flycatchers, 
swallows,  and  warblers,  prey  to  some  extent  upon  useful  para- 
sitic insects,  but,  on  the  whole,  the  habits  of  these  insectivorous 
birds  are  productive  of  considerable  good.  Together  with  the 
vireos,  cuckoos,  and  woodpeckers  (exclusive  of  the  sapsuckers), 
they  are  the  most  valuable  conservators  of  fohage  on  the  farms. 
The  quail,  meadow-lark,  orchard  oriole,  mocking'-bird,  house  wren, 

1  Bulletin  No.  17  of  the  Division  of  the  Biological  Survey  of  the  United  States 
Department  of  Agriculture. 


630  COLLEGE  ZOOLOGY 

grasshopper  sparrow,  and  chipping  sparrow  feed  on  insects  of 
the  cultivated  fields,  particularly  during  the  breeding  season, 
when  the  nestlings  of  practically  all  species  eat  enormous  num- 
bers of  caterpillars  and  grasshoppers. 

"  The  most  evident  service  is  the  wholesale  destruction  of 
weed  seed.  Even  if  birds  were  useful  in  no  other  way,  their 
preservation  would  still  be  desirable,  since  in  destroying  large 
quantities  of  weed  seed  they  array  themselves  on  the  side  of  the 
Marshall  Hall  farmer  against  invaders  that  dispute  with  him, 
inch  by  inch,  the  possession  of  his  fields.  The  most  active  weed 
destroyers  are  the  quail,  dove,  cow-bird,  red- winged  blackbird, 
meadow-lark,  and  a  dozen  species  of  native  sparrows.  The  util- 
ity of  these  species  in  destroying  weed  seed  is  probably  at  least 
as  great  wherever  the  birds  may  be  found  as  investigation  has 
shown  it  to  be  at  Marshall  Hall." 

h.  Domesticated  Birds 

Birds  have  for  many  centuries  been  under  the  control  of  man, 
and  have  produced  for  him  hundreds  of  millions  of  dollars'  worth 
of  food  and  feathers  every  year.  The  common  hen  was  prob- 
ably derived  from  the  red  jungle-fowl,  Gallus  gallus,  of  northeast- 
ern and  central  India.  The  varieties  of  chickens  that  have  been 
derived  from  this  species  are  almost  infinite. 

The  domestic  pigeons  are  descendants  of  the  wild,  blue-rock 
pigeon  Columba  livia  (Fig.  470),  which  ranges  from  Europe 
through  the  Mediterranean  countries  to  central  Asia  and  China. 
Breeders  have  produced  over  a  score  of  varieties  from  this  ances- 
tral species,  such  as  the  carriers,  pouters,  fantails,  and  tumblers. 
Young  pigeons,  called  squabs,  constitute  a  valuable  article  of 
food. 

Of  less  importance  are  the  geese,  ducks,  turkeys,  peacocks, 
swans,  and  guinea-fowls.  The  geese  are  supposed  to  be  derived 
from  the  gray-lag  goose,  Anser  anser,  which  at  the  present  time 
nests  in  the  northern  British  Islands.  Most  of  our  domestic 
breeds  of  ducks  have  sprung  from  the  mallard,  A  nas  boscas.     This 


CLASS  AVES  631 

beautiful  bird  inhabits  both  North  America  and  temperate 
Europe  and  Asia.  The  common  peacock,  Paw  cristatus,  of  the 
Indian  peninsula,  Ceylon,  and  Assam,  has  been  in  domestication 
at  least  from  the  time  of  Solomorr.  It  has  been  distributed  by 
man  over  most  of  the  world.  The  swan  is,  like  the  peacock, 
used  now  chiefly  as  an  ornament.  The  mute  swan,  Cygnus  olor, 
of  Central  Europe  and  Central  Asia,  is  the  common  domesticated 
species.  The  guinea-fowl,  Numida  meleagris,  is  a  native  of  West 
Africa.  Farmers  usually  keep  a  few  of  them  to  "  frighten  away 
the  hawks." 

The  turkey  is  a  domesticated  bird  that  has  been  brought  under 
control  within  the  past  four  centuries.  Our  Puritan  ancestors 
found  the  wild  turkey  abundant  in  New  England.  It  was  intro- 
duced into  Europe  early  in  the  sixteenth  century  and  soon  be- 
came a  valuable  domestic  animal.  In  its  wild  state,  it  is  now 
almost  extinct  except  in  some  of  the  remoter  localities.  Our 
domestic  turkeys  are  descendants  of  the  Mexican  wild  turkey. 


CHAPTER    XXI 
SUBPHYLUM    VERTEBRATA:    CLASS    VII.    MAMMALIA 

The  mammals  are  popularly  known  as  ''  animals."  The  name 
of  the  class  is  derived  from  the  fact  that  most  mammals  possess 
mammary  glands  which  secrete  milk  for  the  nourishment  of  their 
young.  Mammals  also  possess  a  covering  of  hair  at  some  time 
in  their  existence  and  are  distinguished  by  this  characteristic  a^ 
certainly  as  birds  are  by  their  feathers.  With  few  exceptions 
adult  mammals  are  provided  with  at  least  a  small  number  of 
hairs. 

The  seventy-five  hundred  or  more  species  of  living  mammals, 
and  the  three  thousand  or  more  species  of  fossil  mammals  may 
be  grouped  into  two  subclasses,  (i)  Prototheria,  or  egg-laying 
mammals,  and  (2)  Eutheria,  or  viviparous  mammals. 

The  three  living  genera  of  the  Prototheria  are  included  in 
one  order  which  is  confined  to  Australia,  Tasmania,  and  New 
Guinea.     They  are  the  spiny  ant-eater  and  duckbills  (Fig.  513). 

The  Eutheria  may  be  grouped  into  two  divisions :  — 

I.  DiDELPHiA,  or  marsupials,  such  as  the  opossum  and  kanga- 
roo, with  a  pouch  in  which  the  young  are  carried  after  birth,  and 
without  a  typical  placenta  (see  p.  614). 

II.  MoNODELPHiA,  or  placcntals,  with  a  typical  placenta 
before  birth,  and  more  highly  developed  young. 

The  MoNODELPHiA  may  be  subdivided  into  four  sections:  — 

(A)  Unguiculata,  or  clawed  mammals,  such  as  the  moles, 
bats,  dogs,  cats,  seals,  squirrels,  mice,  ant-eaters,  and  sloths. 

(B)  Primates,  with  fingers  usually  terminating  in  "  nails," 
such  as  the  lemurs,  monkeys,  apes,  and  man. 

632 


CLASS   MAMMALIA 


633 


(C)  Ungulata,  or  hoofed  animals,  such  as  the  pigs,  deer, 
sheep,  oxen,  horses,  and  elephants,  and 

(D)  Cetacea,  or  whales,  which,  have  probably  been  derived 
from  the  unguiculat^  division. 

I.  The  Rabbit 

The  rabbit  belongs  to  the  order  of  gnawing  mammals  —  the 
RoDENTiA  or  Glires.  This  order  is  made  up  of  a  number  of 
families,  one  of  which,  the  Leporid^e,  contains  about  sixty  species 
of  rabbits  and  hares.     Rabbits  are  generally  common  in  North 


Fig.  510 


Lateral  view  of  skeleton  wii  1 1       i    1 

(From  Parker  and  HaswcU.) 


America,  both  wild  and  in  a  state  of  domestication.  They  are, 
therefore,  usually  easy  to  obtain.  This  fact  together  with  their 
convenient  size  have  made  them  favorite  objects  for  the  intro- 
duction of  students  to  mammalian  anatomy.  The  following 
account,  however,  is  not  intended  as  a  laboratory  guide,  but  sim- 
ply as  a  means  of  pointing  out  some  of  the  more  obvious  mam- 
malian characteristics  with  the  aid  of  an  animal  that  can  be 
examined  easily  in  the  class  room. 

External  Features. — The  rabbit  (Fig.  510)  is  a  four- 
footed  animal  (quadruped)  adapted  for  leaping.  It  possesses 
an  external  covering  of  hair,  two  large  external  ears,  or  pinnce, 


634  COLLEGE  ZOOLOGY       ) 

and  separate  genital  and  anal  apertures.  The  mouth  is  bounded 
by  soft,  fleshy  lips  which  aid  in  seizing  and  holding  food.  At 
the  end  of  the  snout  are  two  obvious  slits,  the  nostrils.  The 
large  eyes,  one  on  either  side  of  the  head,  are  protected  by  an 
upper  and  a  lower  eyelid  bordered  by  thin  eyelashes,  and  a  white, 
hairless  third  eyelid,  or  nictitating  membrane,  which  may  be 
drawn  over  the  eyeball  from  the  anterior  angle.  Above  and 
below  the  eyes  and  on  either  side  of  the  snout  are  long,  sensitive 
hairs,  the  whiskers  or  vihrissce. 

The  trunk  may  be  separated  into  an  anterior  portion,  the  tho- 
rax, which  is  supported  laterally  by  the  ribs,  and  a  posterior 
portion,  the  abdomen.  The  tail  is  short.  Beneath  it  is  the  anus, 
and  just  in  front  of  this  is  the  urinogenital  aperture.  On  either 
side  of  the  anus  and  just  anterior  to  it  is  a  hairless  depression, 
the  perineal  pouch  into  which  a  strong-smelling  secretion  is 
poured  by  the  perinaeal  glands.  Four  or  five  pairs  of  small 
papillae,  the  teats  or  mammce,  are  situated  in  pairs  on  the  ventral 
surface  of  the  thorax  and  abdomen.  At  the  end  of  the  teats 
open  the  ducts  of  the  mammary  or  milk  glands. 

The /ore  limbs  of  the  rabbit  are  used,  as  in  the  frog,  for  holding 
up  the  anterior  part  of  the  body.  They  possess  five  clawed  digits 
each.  The  hind  limbs  are  longer  and  more  powerful  than  the 
fore  limbs  and  serve  as  leaping  organs.  They  are  provided  with 
only  four  digits;  the  one  corresponding  to  the  great  toe  in  man 
is  absent.  The  rabbit  places  the  sole  of  its  foot  upon  the  ground, 
and  is,  therefore,  said  to  be  plantigrade  (L.  planta,  the  sole  of  the 
foot;    gradior,  walk). 

The  Skeleton.  —  An  outline  of  the  skeleton  is  shown  in  Fig. 
510.  It  consists  principally  of  bone,  but  a  small  amount  of 
cartilage  is  also  present.  As  in  the  fishes,  amphibians,  reptiles, 
and  birds,  there  are  cartilage-bones,  preformed  in  cartilage,  and 
membrane-bones,  arising  by  the  ossification  of  dermal  portions 
of  the  skin.  A  third  type,  called  sesamoid  bones,  occurs  in  the 
tendons  of  some  of  the  limb-muscles,  the  action  of  which  they 
modify;   for  example,  the  knee-cap. 


CLASS  MAMMALIA 


635 


The  axial  skeleton  consists,  as  in  the  pigeon,  of  a  skull,  ribs, 
sternum,  and  vertebral  column.  The  skull  (Fig.  511)  is  formed 
of  both  cartilage-  and  membrane-bones,  and  only  a  small  amount 
of  cartilage.  The  individual  bone&  are  immovably  united  to  one 
another,  and  their  boundaries  are  in  many  cases  obliterated  in 
the  adult  and  can  only  be  made  out  in' the  embryo.  The  follow- 
ing points  are 
worthy  of  special  1 

mention.  The 
occipital  ring  is 
completely  ossi- 
fied and  'there  are 
two  occipital  con- 
dyles (Fig.  511, 
20) ;  the  cranial 
and  olfactory 
cavities  are  sepa- 
rated by  a  bony 
cribiform  plate ; 
the  lower  jaw  (77) 
articulates  di- 
rectly with  the 
squamosal  {g)  ; 
three    small    but 

distinct  auditory  ossicles  are  present;    and  there  is  no  distinct 
parasphenoid  on  the  under  surface. 

The  teeth  are  cutaneous  structures,  as  are  the  scales  and  teeth 
of  the  dogfish-shark  (p.  424),  and  are  developed  from  the  mucous 
membrane  of  the  mouth.  Each  tooth  possesses  an  outer,  hard 
covering,  called  enamel,  a  central  softer  substance,  called  den- 
tine, and  about  the  base  and  in  the  surface  folds  a  bony  layer, 
the  cement.  The  teeth  of  the  rabbit  remain  open  at  the  base  and 
continue  to  grow  throughout  life,  thus  supplying  new  material 
to  replace  that  worn  away  in  grinding  its  vegetable  food. 

The  rabbit  lacks  canine  teeth,  and  the  incisors  (Fig.  511,  74,  id) 


Fig.  si  I.  —  Side  view  of  skull  of  the  rabbit,  i,  nasal 
bone;  2,  lachrymal  bone;  3,  orbito-sphenoid;  4,  frontal; 
5,  optic  foramen;  6,  orbital  groove  for  trigeminal  nerve; 
7,  zygomatic  process  of  squamosal;  8,  parietal;  q,  squa- 
mosal; 10,  supra-occipital;  //,  tympanic  bones;  12,  ex- 
ternal auditory  meatus;  14,  lower  incisor;  15,  anterior 
premolar;  16,  anterior  upper  incisor;  77.  mandible; 
18,  maxilla;  ig,  premaxilla;  20,  occipital  condyle. 
(From  Shipley  and  MacBride.) 


62^6  COLLEGE  ZOOLOGY 

are  widely  separated  from  the  grinding  teeth  {ij).  There  are 
two  pairs  of  incisors  {i6)  lodged  in  sockets  (alveoli)  in  the  pre- 
maxillae  of  the  upper  jaw,  and  one  pair  {14)  projecting  forward 
from  the  anterior  end  of  the  lower  jaw.  Only  the  outer,  curved 
surface  of  the  incisors  is  covered  with  enamel,  and  since  the 
inner  dentine  wears  away  more  rapidly  than  the  enamel,  a  chisel- 
shaped  form  results  that  is  admirably  fitted  for  gnawing.  The 
grinding  teeth  are  called  premolars  and  molars.  The  premolars 
develop  after  a  preceding  set  of  "  milk  "  teeth  have  fallen  out; 
the  molars  have  no  deciduous  predecessors.  The  upper  jaw 
contains  three  pairs  of  anterior  premolars  and  three  pairs  of 
posterior  molars.  The  last  molar  is  smaller  than  the  others. 
The  lower  jaw  is  provided  with  two  pairs  of  premolars  and  three 
pairs  of  molars;   the  last  molar  is  small. 

The  vertebral  column,  as  in  other  vertebrates,  supports  the 
body,  and  protects  the  spinal  cord.  The  vertehrce  move  upon  one 
another;  are  separated  by  intervertebral  disks  of  fibrocartilage, 
except  in  the  sacrum;  and  are  connected  by  intervertebral  liga- 
ments. The  vertebrae  of  the  neck,  or  cervical  vertebrce,  are  al- 
most always  seven  in  number;  those  of  the  chest,  the  thoracic 
vertebrcB,  bear  movably  articulated  ribs;  those  of  the  trunk 
region  are  called  lumbar  vertebrce;  the  three  or  more  sacral  ver- 
tebrcB  are  fused  together  and  support  the  pelvis;  and  the  caudal 
vertebrce,  about  sixteen  in  number,  form  the  skeletal  axis  of  the 
tail. 

The  ribs  and  sternum  constitute  the  framework  of  the  thorax, 
and  not  only  protect  the  vital  organs  in  that  region,  but  also 
play  an  important  role  in  respiration.  There  are  twelve,  or 
sometimes  thirteen,  pairs  of  ribs  (Fig.  510).  The  first  seven 
pairs  articulate  with  the  sternum;  the  others  do  not  reach  the 
sternum.  The  sternum  is  a  long,  laterally  compressed  structure 
consisting  mostly  of  bone.  It  is  situated  in  the  ventral  wall  of 
the  thorax,  and  is  transversely  divided  into  six  segments,  or 
sternebrae. 

The  pectoral  girdle  consists  of  two  scapulae,  two   imperfect 


CLASS   MAMMALIA  637 

clavicles,  and  two  knob-like  coracoids.  Each  half  of  the  pelvic 
girdle  is  called  an  innominate  bone,  and  is  made  up  of  the  ilium, 
ischium,  and  pubis  fused  together.  The  concavity  in  the  in- 
nominate bone  in  which  the  head  of  the  femur  articulates  is 
called  the  acetabulum. 

The  ankle-joint  of  the  rabbit  lies  between  the  tibia  and  fibula 
above,  and  the  tarsal  bones  below.  The  fourth  and  fifth  carpal 
bones  and  corresponding  tarsal  bones  are  fused  together,  forming, 
in  the  fore  limb,  the  unciform  bone,  and  in  the  hind  limb  the 
cuboid  bone.  One  of  the  sesamoid  bones  of  the  hind  limb  which 
is  situated  on  the  front  of  the  distal  end  of  the  femur  is  called 
the  kneepan,  or  patella.  The  tibiale  is  fused  with  the  inter- 
medium of  the  tarsus  to  form  the  astragalus;  and  the  fibular e, 
which  lies  along  its  outer  side,  is  called  the  calcaneum. 

Internal  Anatomy.  —  Unlike  other  vertebrates,  the  body- 
cavity  of  the  rabbit  and  mammals  in  general  is  divided  by  a 
transverse  muscular  partition,  called  the  diaphragm,  into  two 
parts,  an  anterior  thoracic  portion  containing  the  heart  and 
lungs,  and  a  posterior  portion  containing  the  abdominal  viscera. 

The  Digestive  System.  —  The  mouth  or  buccal  cavity  bears 
on  the  anterior  portion  of  the  roof  a  series  of  transverse  ridges 
against  which  the  tongue  works.  That  part  of  the  roof  which 
has  a  bone  foundation  is  known  as  the  hard  palate.  Posterior 
to  this  is  a  muscular  flap,  the  soft  palate,  which  separates  the 
mouth  from  the  pharynx.  At  the  sides  of  the  posterior  part  of 
the  soft  palate  are  a  pair  of  small  masses  of  lymphoid  tissue 
containing  pits  of  unknown  function,  called  the  tonsils.  The 
tongue  is  attached  to  the  floor  of  the  mouth.  It  bears  a  number 
of  taste  papillce  on  the  anterior  part  and  sides.  The  two  orifices 
of  the  eustachian  tubes  and  the  two  apertures  of  the  nasopalatine 
canals,  which  connect  the  nasal  and  buccal  cavities,  are  situated 
in  the  roof  of  the  mouth  behind  and  above  the  soft  palate.  There 
are  four  pairs  of  salivary  glands:  (i)  the  parotids,  (2)  the  infra- 
orbitals, (3)  the  submaxillaries,  and  (4)  the  sublinguals.  They 
pour  their  secretions  into  the  mouth  cavity. 


638  COLLEGE  ZOOLOGY 

The  posterior  continuation  of  the  mouth  cavity  is  called  the 
pharynx.  In  the  floor  of  the  pharynx  is  the  respiratory  opening, 
the  glottis,  which  is  covered  by  a  bilobed  cartilaginous  flap, 
the  epiglottis,  during  the  act  of  swallowing.  The  pharynx  leads 
into  the  narrow,  muscular  oesophagus.  Following  this  is  the 
stomach;  then  comes  the  U-shaped  duodenum,  into  which  the 
pancreatic  duct  from  the  pancreas  and  the  bile  duct  from 
the  liver  open. 

The  small  intestine,  which  is  seven  or  eight  feet  in  length,  leads 
into  the  colon,  which  is  continued  as  the  rectum.  At  the  an- 
terior end  of  the  colon  a  large,  thin-walled  tube,  the  ccecum,  is 
given  off.  This  caecum  is  about  an  inch  in  diameter  and  twenty 
inches  long;  it  ends  in  a  thick- walled,  finger-hke  process  about 
four  inches  long,  called  the  vermiform  appendix.  A  large  caecum 
is  characteristic  of  most  herbivorous  animals  with  simple 
stomachs. 

The  rabbit  possesses  the  following  ductless  glands :  the  spleen, 
the  thymus,  the  thyroid,  and  the  suprarenals. 

The  Circulatory  System.  —  The  blood  corpuscles  of  the 
rabbit  are  unlike  those  of  the  lower  vertebrates,  being  smaller, 
round  instead  of  oval,  biconcave,  and  without  nuclei.  The 
heart  is  four  chambered,  as  in  the  pigeon,  but  the  main  blood- 
vessel, the  aorta,  arising  from  the  left  ventricle,  has  only  the  left 
arch,  whereas  in  birds  the  right  arch  persists.  The  right  sys- 
temic arch  of  the  rabbit  is  represented  by  the  innominate  artery, 
which  is  the  common  trunk  of  the  right  carotid  and  subclavian 
arteries.  An  hepatic-portal  system  is  present,  but  no  renal-portal 
system. 

The  lymphatic  system  is  important  in  rabbits  and  other  mam- 
mals. The  fluid  portion  of  the  blood,  which,  because  of  the 
blood  pressure,  escapes  through  the  walls  of  the  capillaries  into 
the  spaces  among  the  tissues,  is  collected  into  lymph  vessels. 
These  vessels  pass  through  so-called  lymph  glands,  and  finally 
empty  into  the  large  veins  in  the  neck.  The  lymphatics 
which  collect  nutriment  from  the  intestine  are  called  lacteals. 


CLASS   MAMMALIA  639 

The  Respiratory  System.  —  The  rabbit  and  all  other 
mammals  breathe  air  by  means  of  lungs.  The  glottis  opens  into 
the  larynx,  from  which  a  tube  caljed  the  trachea  or  windpipe 
arises.  The  trachea  is  held  open  by  incomplete  rings  of  cartilage; 
it  divides  into  two  bronchi,  one  bronchus  going  to  each  lung. 
The  larynx  is  supported  by  a  number  of  cartilages  and  across  its 
cavity  extend  two  elastic  folds  called  the  vocal  cords.  The  lungs 
are  conical  in  shape,  and  lie  freely  in  the  thoracic  cavity  sus- 
pended by  the  bronchi. 

Air  is  drawn  into  the  lungs  by  the  enlargement  of  the 
thoracic  cavity.  This  is  accomplished  both  by  pulling  the  ribs 
forward  and  then  separating  them,  as  in  most  reptiles,  and  by 
means  of  the  diaphragm.  The  diaphragm  is  normally  arched 
forward  and  when  it  contracts  it  flattens,  thus  enlarging 
the  thoracic  cavity.  The  increased  size  of  this  cavity  results 
in  the  expansion  of  the  lungs,  because  of  the  air  pressure 
within  them,  and  the  inspiration  of  air  through  the  nostrils. 
Air  is  pumped  out  of  the  lungs  (expiration)  by  the  contraction 
of  the  elastic  pulmonary  vesicles,  and  of  the  thoracic  wall  and 
diaphragm. 

The  Excretory  System.  —  The  urine  excreted  by  the  two 
kidneys  is  carried  by  two  slender  tubes,  the  ureters,  into  a  thin- 
walled,  muscular  sac,  the  urinary  bladder.  At  intervals  the  walls 
of  the  bladder  contract,  forcing  the  urine  out  of  the  body  through 
the  urino genital  aperture. 

The  Nervous  System.  —  The  rabbit  possesses  a  brain,  cranial 
nerves,  spinal  cord,  spinal  nerves,  and  a  sympathetic  nervous 
system. 

The  brain  (Fig.  512),  as  in  other  mammals,  differs  from  that 
of  the  lower  vertebrates  in  the  large  size  of  the  cerebral  hemi- 
spheres (f.b)  and  cerebellum  (h.b).  The  cerebral  hemispheres  are 
slightly  marked  by  depressions,  or  stilci,  which  divide  the  surface 
into  lobes  or  convolutions  not  present  in  the  pigeon.  The 
olfactory  lobes  (b.o)  are  very  large  and  club-shaped.  The  optic 
lobes  are  each  divided  by  a  transverse  furrow  into  two.     The 


640  COLLEGE  ZOOLOGY 

cerebellum  is  divided  into  three  parts,  a  central  portion  {cb') 
and  two  lateral  lobes. 

The  Sense  Organs.  —  The  eyes  of  mammals  are  without 
a  pecten  such  as  is  present  in  birds.  The  large  outer  ear,  or 
pinna,  serves  to  collect  sound  waves;  the  middle  ear  transmits 
the  vibrations  of  the  tympanic  membrane,  or  eardrum,  by  means 
of  three  auditory  ossicles,  which  extend  across  the  tympanic 
cavity,  to  the  inner  ear.     The  cochlea  of  the  inner  ear  is  spirally 

0 


1 
X   xi  ^ 

1      *"•/•  ii      fiJ,  P-v.  vi    vii   ix       xii 

Fig.  512.  —  Side  view  of  brain  of  the  rabbit,  h.o,  olfactory  bulb;  ch',  supe- 
rior vermis  of  cerebellum;  f.b,  cerebral  hemisphere;  h.b,  cerebellum;  h.l,  hippo- 
campal  lobe;  m.d,  medulla  oblongata;  p.v,  pons  Varolii;  r.J,  rhinal  fissure; 
i-xii,  cranial  nerves.     (From  Wiedersheim.) 

coiled,  and  not  simply  curved  as  in  the  pigeon.  The  nasal 
cavities  are  very  large,  indicating  a  highly  developed  sense  of 
smell. 

The  Reproductive  System.  —  The  two  testes  of  the  male 
lie  in  oval  pouches  of  skin,  called  scrotal  sacs,  one  on  either  side  of 
the  copulatory  organ,  or  penis.  They  may  be  drawn  back  into 
the  abdominal  cavity  through  the  narrow  inguinal  canals.  The 
spermatozoa  pass  from  the  testes  into  irregular  convoluted  tubes 
called  the  epididymes ;  they  then  enter  the  vasa  deferentia  which 
lead  into  the  abdominal  cavity  and  open  into  a  medium  sac, 
the  uterus  masculinus,  attached  to  the  dorsal  surface  of  the  urino- 
genital  canal,  or  urethra.  During  copulation  the  spermatozoa 
pass  into  the  urethra  and  are  transferred  to  the  female  by  the 
penis.     Surrounding   the   vasa   deferentia   is   a   prostate   gland 


CLASS   MAMMALIA  641 

which  opens  by  short  ducts  into  the  urethra,  and  just  behind 
are  a  pair  of  Cowper's  glands.  The  secretions  from  these  glands 
are  added  to  the  spermatozoa,  making  the  seminal  mass  more 
fluid. 

The  two  ovaries  of  the  female  are  oval  bodies  exhibiting  small, 
rounded  projections  on  the  surface;  these  are  the  outlines  of  the 
Graafian  follicles^  each  of  which  contains  an  ovum.  The  ovi- 
ducts consist  of  an  anterior  Fallopian  tube  and  a  middle  uterus; 
the  uteri  unite  posteriorly  to  form  the  vagina.  The  anterior 
end  of  the  Fallopian  tube  is  wide  and  funnel-shaped;  it  carries 
the  ova  from  the  ovary  to  the  uterus,  where  the  young  are 
developed.  The  urinogenital  canal,  or  vestibule,  is  a  wide, 
median  tube.  On  its  ventral  wall  lies  a  small  rod-like  body,  the 
clitoris,  corresponding  to  the  penis  of  the  male. 

The  ova  undergo  holoblastic  segmentation  in  the  oviduct;  they 
then  pass  into  the  uterus,  where  they  receive  nourishment  from 
the  blood  of  the  mother  through  a  structure  called  the  placenta, 
which  is  formed  from  the  foetal  membranes  and  imited  with  the 
mucous  membrane  of  the  uterine  wall.  The  interval  between 
fertilization  and  birth,  known  as  the  period  of  gestation,  is  thirty 
days.  Eight  or  ten  young  may  be  produced  at  a  birth,  and  a 
new  litter  may  be  born  every  month  for  a  large  part  of  the  year. 
Young  rabbits  breed  when  three  months  old. 

2.   A  Brief  Classification  of  Living  Mammals^ 

As  stated  on  page  632,  there  are  about  seventy- five  hundred 
species  of  living  mammals,  and  three  thousand  or  more  species  of 
fossil  forms  known  to  man.  The  living  mammals  may  be 
grouped  into  two  subclasses  and  eighteen  orders. 

Class  Mammalia. — Mammals  or  "Animals." — Warm- 
blooded vertebrates  with  a  covering  of  hair  at  some  stage  in  their 
existence,  and  with  cutaneous  glands  in  the  female,  which  secrete 
milk  for  the  nourishment  of  the  young. 

1  Modified  from  Osbom's  Age  of  Mammals. 
2  T 


642  COLLEGE  ZOOLOGY 

Subclass  I.   Prototheria.     Egg-laying  Mammals. 

Order  I.  Monotremata.  —  Monotremes. — Examples:  Or- 
nithorhynchus,  duckbill  (Fig.  513);   Echidna,  spiny  ant- 
eater. 
Subclass  II.  Eutheria. — Viviparous  Mammals. 
Division  I.   Didelphia  (Metatheria)  .  —  Marsupials. 

Order  i.   Marsupialia. — Marsupials. — Mammals  which 
usually  carry  their  young  in  a  marsupium  or  pouch; 
allantoic  placenta  usually  absent. 
Suborder    i.    Polyprotodontia.  —  Chiefly    Carnivo- 
rous Marsupials.  — Marsupials  with  eight  or  ten  in- 
cisors in  the  upper  jaw,  and  at  least  three  pairs  in  the 
lower  jaw.     Examples:  Z)iJe//>/M*5,  opossum  (Fig.  514); 
Thylacomys,  rabbit  bandicoot. 
Suborder    2.   Diprotodontia.  —  Mostly  Herbivorous 
Marsupials.  —  Marsupials  with  not  more  than  three 
pairs  of  incisors  in  the  upper  jaw,  and  usually  one  pair 
of  large  incisors  in  the  lower  jaw.     Examples:  Coeno- 
lesies,  caenolestes;    Phalanger,  cuscus;    Macropus,  kan- 
garoo and  wallaby  (Fig.  515). 
Division  II.   Monodelphia    (Placentalia,    Eutheria).  — 
Eutheria   nourished   before   birth  by  a  typical  pla- 
centa; young  never  carried  in  a  pouch. 
Section  A.   Unguiculata.  —  Clawed  Mammals. 

Order  i.  Insectivora. — Insectivores. — Small,  usually 
terrestrial,  clawed  mammals;  feet  plantigrade,  generally 
pentadactyle;  molars  enamelled,  tuberculated,  and 
rooted.  Examples:  Erinaceus,  hedgehog;  Condylura, 
star-nosed  mole;    Sorex,  shrew  (Fig.   516). 

Order  2.  Dermoptera. — Dermoptera. — Two  genera  of 
flying  mammals  resembling  insectivores  in  the  structure 
of  the  skull  and  the  canine  teeth.  They  inhabit  the 
forests  of  Malaysia  and  Philippine  Islands,  and  are 
popularly  called  flying  lemurs. 

Order  3.   Chiroptera. — Bats. — Clawed  mammals  with  fore 


CLASS  MAMMALIA  643 

limbs  modified  for  flight.  Examples:  Pteropus,  flying 
fox;  Desmodus,  blood-sucking  Y3impiTt\  Myotis,  hrown 
bats  (Fig.  517). 

Order  4.  Carnivora  (Fer^e)  . — Flesh-eating  Mammals.  — 
Clawed  carnivorous  mammals  with  large,  projecting 
canine  teeth;  incisors  small;  premolars  adapted  for 
cutting  flesh. 
Suborder  i .  Fissipedia.  —  Chiefly  Terrestrial  Carni- 
vores. —  Chiefly  terrestrial  carnivores  with  separated 
digits.  Examples:  Canis,  dog,  fox,  etc.;  Procyon, 
raccoon  (Fig.  519);  Mephitis,  skunk  (Fig.  520);  HycRfiaj 
hyaena;  Felis,  cat,  lion,  etc. 
Suborder  2.  Pinnipedia.  —  Seals  and  Walruses.  — 
Aquatic  carnivores  with  digits  united  by  a  membrane. 
Examples:  Zalophus,  California  sea  lion;  Callotaria,  fur 
seal;  Phoca,  harbor  seal;  Odobcenus,  walrus  (Fig.  521). 

Orders.  Rodentia  (Glires).  —  Rodents  or  Gnawing 
Animals. 
Suborder  i.  Duplicidentata. — Hares  and  Picas. — 
Rodents  with  two  pairs  of  incisors  in  the  upper  jaw. 
Examples:  Lagomys,  pic3i;  Lepus,  cottonta,i\. 
Suborder  2.  Simplicidentata.  —  Rodents  Proper.  — 
Rodents  with  one  pair  of  incisors  in  the  upper  jaw. 
Examples:  Sciurus,  squirrel;  Castor,  beaver;  Geomys, 
pocket  gopher  (Fig.  523);  Mm5,  mice,  rats;  Erethizon, 
Canada  porcupine;    Cavia,  guinea  pig. 

Order  6.  Edentata.  —  American  Edentates.  —  Clawed 
EuTHERiA  without  enamel  on  the  teeth;  teeth  absent 
from  anterior  part  of  jaw.  Examples:  Myrmecophaga, 
great  ant-eater  (Fig.  525);  Brady  pus,  three-toed  sloth; 
Tatusia,  nine-banded  armadillo  (Fig.  526). 

Order  7.  Pholidota.  —  Scaly  Ant-eaters.  —  Clawed  Eu- 
THERIA  with  a  covering  of  large,  overlapping,  horny 
scales;  teeth  absent;  tongue  long  and  protractile. 
Example:    Manis,  pangolin  (Fig.  527), 


644  COLLEGE  ZOOLOGY 

Order  8.    Tubulidentata.  —  Aard    Varks.  —  One    genus, 
Oryderopus,  with  two  species  of  burrowing  mammals, 
confined  .  to    Africa.      They   are    called    Cape    ant- 
eaters. 
Section  B.   Primates.^  —  Mammals  with  "Nails." 

Order  9.    Primates. — Lemurs,    Monkeys,    Man. — Eu- 
THERiA  with  "  nails  ";  great  toe  or  thumb  or  both  are 
opposable  to  other  digits;  brain  large. 
Suborder  i.  Lemuroidea.  — Lemuroids.  — Primates  with 
front  teeth  separated  by  a  space  in  the  middle  line. 
Example:    Lemur,  lemur  (Fig.  528). 
Suborder  2.  Anthropoidea.  —  Monkeys,  Apes,  Man.  — 
Primates  with  front  teeth  in  contact  in  middle  line. 
Ejtamples:    Cehus,  capuchin;    A  teles,  spider  monkeys 
(Fig.  530);    Cynocephalus,  baboon;  Simia,  orang-utan 
(Fig.  532);   Gorilla,  gorilla  (Fig.  533);    Homo,  man. 
Section  C.   Ungulata.    Hoofed  Mammals. 

Order  10.  Artiodactyla. — Even-toed  Ungulates. — Un- 
gulata with  an  even  number  of  digits;  the  axis  of 
symmetry  passes  between  digits  three  and  four.  Ex- 
amples: Sus,  pig;  Dicotyles,  peccary;  Hippopotamus, 
hippopotamus;  Camelus,  camel;  Girafa,  giraffe; 
Cervus,  deer,  etc.;  Alces,  moose;  Bos,  domestic  cattle; 
Bison,  bison  (Fig.  536). 

Order  11.  Perissodactyla. — Odd-toed  Ungulates. — Un- 
gulata with  an  uneven  number  of  digits;  the  axis  of 
symmetry  passes  through  digit  three.  Examples: 
Equus,  horse,  ass,  zebra;  Tapirus,  tapir  (Fig.  538); 
Rhinoceros,  rhinoceros  (Fig.  539). 

^  The  position  of  the  Primates  in  the  midst  of  the  mammalian  series  instead  of 
at  the  end,  where  they  are  usually  placed,  may  seem  strange  to  students,  but  man, 
the  apes,  and  other  mammals  belonging  to  this  group  retain  a  larger  number  of 
primitive  characters  than  do  the  orders  that  are  placed  above  them  in  this  classi- 
fication. The  primates  excel  principally  in  the  development  of  the  nervous  system, 
but  are  comparatively  primitive  when  the  bones,  muscles,  teeth,  and  other  organs 
are  taken  into  account. 


CLASS  MAMMALIA  645 

Order  12.  Proboscidea.  —  Elephants. — Ungulata  with 
long,  prehensile  proboscis ;  incisors  form  tusks; 
molars  very  broad.  Examples:  Elephas,  Asiatic  ele- 
phant;   Loxodonta,  African  elephant  (Fig.  540). 

Order  13.  Sirenia.  —  Sea-cows. — Aquatic  Eutheria  of 
the  ungulate  type;  tail  with  horizontal  fin;  fore  limbs 
fin-like;  hind  limbs  absent.  Examples:  Halicore, 
dugong;    Manatus,  manatee  (Fig.   541). 

Order  14.  Hyracoidea. — Hyraces  or  Coneys. — Small  ro- 
dent-like mammals,  with  short  ears  and  reduced  tail; 
fore  limbs  with  four  digits;  hind  limbs  with  three  digits. 
There  is  a  single  living  genus,  Frocavia,  and  about 
eighteen  species,  in  Africa.  One  species,  P.  syriaca, 
reaches  Syria;  it  is  the  coney  of  the  Bible.. 
Section  D.  Cetacea. — Whales  and  Dolphins. — Aquatic 
mammals  probably  derived  from  the  Unguiculata  or 
Ungulata. 

Order  15.  Odontoceti' (Denticeti). — Toothed  Whales. 
Cetacea  with  teeth,  at  least  on  the  lower  jaw;  no 
whalebone.  Examples:  Delphinus,  dolphin  (Fig.  542); 
Phocoena,  porpoise;    Grampus,  grampus. 

Order  16.  Mystacoceti. — Whalebone. Whales. — Cetacea 
without  teeth  in  adult;  mouth  provided  with  plates 
of  whalebone.  Examples:  Balosnoptera,  fin  whale; 
Balcdna,  right  whale. 

3.   A  Review  of  the  Principal  Orders  and  Families  of 
Living  Mammals 

Order  Monotremata. — Egg-laying  Mammals. — The  Mono- 
TREMES  are  primitive  mammals  confined  to  Australia,  New 
Guinea,  and  Tasmania.  Their  most  conspicuous  peculiarity  is 
their  egg-laying  habit,  since  they  are  the  only  mammals  that 
reproduce  in  this  way.  The  two  oviducts  do  not  unite  to  form 
a  vagina,  but  open  into  a  cloaca  along  with  the  intestine  and 
urethra,  as  in  birds  and  reptiles  (hence  the  term  Monotremata: 


646 


COLLEGE  ZOOLOGY 


Gr.  monos,  one;    trema,  an  opening).     In  certain  respects  the 
skeleton  agrees  with  that  of  the  reptiles. 

The  young  before  hatching  live  on  the  yolk  contained  in  the 
egg.  After  hatching,  the  young  are  for  a  time  nourished  by  milk 
from  the  mammary  glands.  These  glands  do  not  open  at  the 
end  of  a  papilla,  or  teat,  but  pour  their  secretions  upon  the  hair 

of  the  abdomen.  The 
young  either  suck  or 
lick  the  milk  from  this 
hair. 

There  are  three 
genera,  each  contain- 
ing a  single  species. 
The  spiny  ant-eater. 
Echidna  aculeata,  is 
from  fifteen  to  eighteen 
inches  in  length.  It 
has  a  prolonged  snout, 
a  mouth  without  teeth, 
an  extensile  tongue, 
and  a  covering  of  stiff 
spines  mixed  with 
long,  coarse  hairs.  It 
lives  in  burrows  and  feeds  upon  ants.  The  egg  is  placed  by  the 
lips  of  the  mother  within  a  fold  of  skin  on  the  abdomen;  here  it 
is  protected  until  hatched.  Proechidna,  the  long-snouted 
echidna,  is  confined  to  New  Guinea. 

The  duckbill  or  platypus,  Ornithorhynchus  anatinus  (Fig.  513), 
is  about  as  large  as  Echidna,  but  is  adapted  for  life  in  the  water. 
It  possesses  webbed  feet,  a  thick  covering  of  waterproof  fur  like 
that  of  a  beaver,  and  a  duck-like  bill  with  which  it  probes  in  the 
mud  under  water  for  worms  and  insects.  The  heels  of  the  male 
are  provided  with  strong  horny  spurs  connected  with  a  duct  from 
a  venom  gland  in  the  thigh.  During  the  daytime  the  duckbill 
sleeps  in  a  grass-lined,  underground  chamber  at  the  end  of  a  long 


Fig.  S13.  —  The  duckbill,  Ornithorhynchus 
anatinus.    (From  Shipley  and  MacBride.) 


CLASS  MAMMALIA 


647 


burrow  in  the  bank,  the  entrance  of  which  is  under  water.     In 
this  chamber  one  or  two  eggs  are  laid  and  the  young  reared. 

Order  Marsupialia.  — Marsupials  or  Pouched  Mammals.  — 
The  Marsupials  occur  mainly  in '  Australia  and  neighboring 
islands,  but  a  few  are  natives  of  America.  Their  method  of 
reproduction  is  peculiar.  The  eggs,  which  are  without  shells, 
absorb  food  from  the  uterus;  they  are  not  laid,  as  in  the  mono- 
tremes,  but  hatch  within 
the  mother's  body  and  the 
young  are  born  in  an  im- 
mature condition.  The 
mother  transfers  them 
with  her  lips  to  a  pouch 
on  the  abdomen,  where 
they  are  fed,  by  means  of 
teats,  upon  milk  from  the 
mammary  glands. 

The  opossums  (Didel- 
PHiiDiE)  and  kangaroos 
and  wallabies  (Macro- 
PODiD^)  are  well-known 
groups.  The  opossimis 
are  confined  to  America. 
There  are  four  genera  and 
about  twenty- five  species; , 
only  one  of  these  is  com- 
mon in  the  United  States, 
the  Virginia  opossum, 
Didelphis  virginiana  (Fig.  514).  The  opossum  occurs  in  the 
Southern  and  Middle  states.  It  sleeps  during  the  day,  usually 
in  a  hollow  tree  or  stump,  but  is  active  at  night,  seeking  insects, 
eggs,  young  birds  and  mammals,  berries,  nuts,  etc.,  which  con- 
stitute its  food.  When  disturbed  the  opossum  frequently  feigns 
death,  or  "  plays  possum."  Two  or  three  litters  of  from  six  to 
fourteen  young  each  are  produced  per  year.     The  young  remain 


Fig.  514. 
giniana. 


—  The   opossum,  Didelphis  vir- 
(Photographed  by  the  author.) 


648 


COLLEGE   ZOOLOGY 


with  the  mother  for  about  two-  months,  at  first  in  the  pouch 
and  later  often  riding  about  on  her  back.  Opossums  are  used 
as  food  in  the  south,  and,  when  properly  roasted,  are  excellent. 

Other  American  marsupials  that  should  be  mentioned  are  the 
murine  opossum,  Marmosa  murina,  which  is  no  bigger  than  a 
mouse;   and  the  yapock,  the  only  member  of  the  genus  Chiro- 

nectes,  which  is  the  size  of  a 
rat,  has  webbed  feet,  and 
lives  in  the  water,  catching 
small  fish,  crustaceans,  and 
aquatic  insects. 

The  kangaroos  and  wal- 
labies (Macropodid^)  are 
represented  by  about  sixty 
species  distributed  all  over 
the  Australian  region.  They 
range  in  size  from  four  or 
five  feet  in  height  to  that 
of  a  small  rabbit.  The  fore 
limbs  are  very  small  and  are 
used  principally  for  grasping 
(Fig.  515),  whereas  the  hind 
limbs  and  tail  are  strongly 
The  rock  wdkb^,  Petrogaie  developed,  enabling  the 
animals  to  move  about 
rapidly  by  a  series  of  leaps. 
The  kangaroos  are  vege- 
tarians, feeding  on  grass,  herbs,  and  roots.  Most  of  them  are 
terrestrial,  but  a  few  are  arboreal.  The  natives  of  Australia 
hunt  them  both  for  sport  and'  for  food.  In  some  localities 
they  are  injurious,  since  they  eat  the  grass  necessary  for  feeding 
the  cattle  and  sheep. 

The  other  families  of  marsupials  are  with  the  exception  of  the 
Epanorthid^,  which  contains  the  South  American  genus 
Cosnolestes,  confined  to  the   Australian   region.     They  are   (i) 


Fig.  51S 

xanthopus,  with  young  in  pouch.  (From 
Shipley  and  MacBride,  after  Vogt  and 
Specht.) 


CLASS  MAMMALIA  649 

the  banded  ant-eaters  (Myrmecobiid^),  (2)  the  pouched  mice, 
dasyures,  and  Tasmanian  devil  (Dasyurid^),  (3)  the  thylacines 
and  sparassodonts  (Thylacynid^e)^  (4)  the  bandicoots  (Pera- 
MELiD^),  (5)  the  pouched  moles  (Notoryctid.e),  (6)  the  pha- 
langers    (Phalangeridje),    and    (7)    the    wombats    (Phasco- 

LOMYID^). 

Order  Insectivora.  —  Insectivores.  — These  are  small  mam- 
mals covered  with  fur.  They  are  considered  the  most  primitive 
of  the  mammals  that  nourish  their  young  before  birth  by  means 
of  a  placenta.  Insectivores  are  entirely  absent  from  the 
Australian  region  and  most  of  South  America.  They  are 
nocturnal  in  habit  and  feed  principally  on  insects  which  they 
seize  with  their  projecting  front  teeth  and  cut  into  pieces  with  the 
sharp-pointed  cusps  on  their  hind  teeth.  Most  of  them  are 
terrestrial,  but  a  number  are  sub  terrestrial  {i.e.  burrow) ;  a  few 
are  aquatic,  and  some  are  arboreal. 

The  two  families  of  insectivores  represented  in  North  America 
are  the  Talpid^,  containing  the  moles  and  shrew  moles,  and 
the  SoRiciD^,  or  shrews.  The  moles  are  stout,  with  short  fore 
legs,  fore  feet  adapted  for  digging,  rudimentary  eyes,  and  with- 
out external  ears.  The  common  mole,  Scalops  aquaticus, 
ranges  from  southern  Canada  to  Florida.  It  burrows  just  be- 
neath the  surface  of  the  ground,  and  is  of  considerable  benefit 
because  of  the  insects  it  destroys,  though  its  upheaved  tunnels 
soon  disfigure  a  lawn.  The  rate  of  progress  underground  is 
astonishing.  One  will  tunnel  a  foot  in  three  minutes,  and  a 
single  specimen  under  normal  conditions  is  known  to  have  made 
a  runway  sixty-eight  feet  long  in  a  period  of  twenty- five  hours. 
(Hornaday.) 

The  shrews  (SoRiciDiE)  have  pointed  heads,  rat-like  feet, 
small  eyes,  a  distinct  neck,  and  small  external  ears.  About 
thirty- five  species  occur  in  North  America  north  of  Mexico; 
some  of  them  are  among  the  smallest  of  all  mammals.  They 
live  in  burrows  or  on  the  surface  of  the  ground.  The  common 
or  long- tailed  shrew,  Sorex  personatus  (Fig.  516),  inhabits  the 


650 


COLLEGE   ZOOLOGY 


northern  part  of  the  United  States.  It  is  about  three  and  three 
quarters  inches  in  length  and  resembles  a  mouse  in  appearance. 
The  short-tailed  shrew,  Blarina  brevicauda,  is  also  a  resident  of 
the  Northern  states. 

Other  families  of  insectivores  are  (i)  the  Madagascar  tenrecs 
(Centetid^e),  (2)  the  solenodonts  (Solenodontid^)  of  Cuba 
and  Haiti,  (3)  the  golden  moles  (Chryso chloride)  of  South 
Africa,  (4)  the  hedgehogs  (Erinaceid^)  of  Europe,  Asia,  and 
North  Africa,  (5)  the  Oriental  tree  shrews  (Tupaiid^)  of  India 


Fig.  516.  — The  long-tailed  shrew,  Sorex  personatus.     (From  Ingersoll.) 


and  Borneo,  and  (6)  the  jumping  shrews  (Macroscelidid^)  of 
Africa. 

Order  Chiroptera.  —  Bats. — The  bats  are  easily  distinguished 
from  other  mammals  by  the  modification  of  their  fore  limbs  for 
flight.  The  fore  arm  and  fingers  are  elongated  and  connected 
with  each  other  and  with  the  hind  feet,  and  usually  the  tail,  by 
a  thin  leathery  membrane.  Because  of  their  remarkable  powers 
of  locomotion  bats  are  very  widely  distributed,  occurring  on 
small  islands  devoid  of  other  mammals.  There  are  more  than 
six  hundred  species  of  bats.  Most  of  them  are  small  and 
chiefly  nocturnal.  During  the  day  they  go  into  retirement  and 
hang  head  downward  suspended  by  the  claws  of  one  or  both  legs. 
At  night  bats  fly  about  actively  in  search  of  insects.  Some  of 
them  live  on  fruit,  and  a  few  suck  the  blood  of  other  mammals. 

The  fruit-eating  bats  (suborder  Megachiroptera;  Family 
PxEROPiDiE)   occur  in   Africa,  Asia,  Australia,  and   the    East 


CLASS   MAMMALIA  65 1 

Indies.  The  largest  of  these  are  the  flying  ^'  foxes  "  (Pteropus). 
One  species  (P.  edulis)  has  a  wing  expanse  of  five  feet  and  a  body- 
only  one  foot  in  length.  The  fruit  feats  feed  on  'fruit,  especially 
figs  and  guava,  and  move  about  in  companies. 

Almost  half  of  all  the  species  of  bats  belong  to  the  family 
Vespertilionid-E.  The  brown  bat,  Vespertilio  fuscus,  is  a  com- 
mon species  inhabiting  the  United  States.  The  little  brown 
bat,  Myotis  lucifugus  (Fig.  517),  is  abundant  in  eastern  North 
America.     It  is  less  than  three  and  a  half  inches  in  length. 


517.  —  The  little  brown  bat,  Myotis  lucifugus.     (From  IngersoU.) 


The  true  vampire  bats  belong  to  the  family  Phyllostomid^  and 
live  in  South  America.  They  live  on  the  blood  of  horses,  cattle, 
and  other  warm-blooded  animals,  and  sometimes  attack  sleeping 
human  beings.  Their  front  teeth  are  very  sharp,  but  the  back 
teeth  have  practically  disappeared.  The  skin  is  cut  by  the 
front  teeth,  and  the  oozing  blood  is  lapped  up. 

Some  of  the  other  families  of  bats  are  (i)  the  long-eared  bats 
(EMBALLONURiDiE) ,  (2)  the  nosclcaf  bats  (Rhinolophid^), 
(3)  the  funnel-eared  bats  (Natalid^),  (4)  the  hare-lipped  bats 
(NocTiLiONiDiE),  (5)  the  MoLOSSiD^,  which  are  more  at  home 
on  their  legs  than  other  bats  and  can  scamper  about  almost  like 
mice,  and  (6)  the  Thyropterid^,  which  have  sucking  discs  on 
the  thumbs  and  soles  of  the  feet,  enabling  them  to  adhere  to  a 
smooth  surface. 


652 


COLLEGE  ZOOLOGV 


Order  Carnivora.  —  Flesh-eating  Mammals.  —  Not  all  of 
the  carnivores  ^  are  flesh-eating ;  many  of  them  are  omniv- 
orous, and  a  few  are  chiefly  vegetarian.  The  teeth  of  car- 
nivores (Fig.  518)  are  perhaps  the  most  characteristic  feature 

of  the  order.  The  front 
teeth,  or  incisors  {i  2),  are 
small  and  of  little  use;  the 
canines  (c),  or  eye-teeth, 
are  very  large  and  pointed, 
enabhng  the  animal  to  cap- 
ture and  kill  its  prey;  the 
premolars  (pm  7,  pm  4)  and 
the  first  molar  in  the  lower 
jaw  {m  i)  have  sharp-cutting 
edges;  the  other  molars  are 
broad,  crushing  teeth;  the 
fourth  premolar  of  the  upper 
jaw  (pm  4)  and  the  first 
molar  of  the  lower  jaw  (m  i)  bite  on  one  another  like  a  pair  of 
scissors,  and  are  called  carnassial  teeth. 

The  living  carnivores  may  be  grouped  into  eleven  families,  of 
which  eight  belong  to  the  suborder  Fissipedia,  or  chiefly  ter- 
restrial Carnivora,  and  three  to  the  suborder  Pinnipedia,  or 
aquatic  Carnivora.  The  five  families  of  Fissipedia  occurring 
in  North  America  north  of  Mexico,  and  the  approximate  number 
of  species  in  each,  are  as  follows  (Hornaday):  — 


Fig.  518.  —  Teeth  of  dog.  i  2,  second 
incisor;  c,  canine;  pm  i,  pm  4,  first  and 
fourth  premolars;  m  i,  first  molar.  (From 
Shipley  and  MacBride.) 


FAMn.Y 

Common  Name 

Approximate  Number  of 
Species  North  of  Mexico 

Canidae 

Dogs 

22 

Procyonidae 

Raccoons 

3 

Ursidae 

Bears 

12 

Mustelidae 

Martens 

46 

Felidae 

Cats 

8 

CLASS   MAMMALIA  653 

The  other  families  are  the  civets  and  mungooses  (ViVERRiDiE) 
of  Europe,  Asia,  and  Africa,  the  aard  wolves  (Protetid.-e)  of 
Africa,  and  the  hyaenas  (Hy^nid^)  of  Africa  and  Asia. 

The  Canid^  are  represented  in  North  America  by  the  wolves 
and  foxes.  These  animals  walk  on  their  toes  (digitigrade), 
possess  blunt,  non-retractile  claws,  and  have  a  more  or  less 
elongated  muzzle.  The  red  fox,  Vulpes  fulvus,  ranges  from 
northern  North  America  south  to  Georgia.  It  is  persistently 
hunted  by  the  poultry  raiser  because  of  its  fondness  for  chickens, 
but  the  benefits  derived  from  the  destruction  of  field  mice, 
rabbits,  ground  squirrels,  woodchucks,  and  insects,  which  con- 
stitute the  larger  part  of  a  fox's  food,  probably  more  than 
repay  the  loss  of  a  few  fowls.  Foxes  seek  their  food  most 
actively  in  the  morning  and  evening  twilight.  They  are 
monogamous;  mate  in  February  and  March;  and  bring  forth, 
on  the  average,  five  young  in  April  or  May.  The  black  phase 
of  the  red  fox  is  called  by  furriers  "  silver  fox,"  and  high  prices 
are  paid  for  skins  of  this  phase.  Skins  of  the  ordinary  red  fox 
bring  from  $1.50  to  $3.50  each,  but  those  of  the  silver  fox  range 
from  $50  to  $250,  and  pure  black  skins  command  from  $500 
to  $2000  each.  Silver  fox  farming  may  be  carried  on  success- 
fully, and  it  seems  probable  "  that  under  proper  management  fox 
raising  will  be  developed  into  a  profitable  industry."     (Osgood.) 

The  arctic,  or  blue  fox,  Vulpes  lagopus,  inhabits  the  Arctic 
regions,  where  it  lives  in  burrows;  and  feeds  on  wild  fowl  and 
small  mammals,  especially  lemmings  and  polar  hares.  In  the 
winter  its  fur  may  become  perfectly  white,  enabling  it  to  creep 
upon  its  prey  unseen.  The  gray  fox,  Urocyon  cmereoargenteus , 
is  the  common  species  in  the  eastern  part  of  North  America.  It 
is  partial  to  the  forests  of  uncultivated  regions,  and  makes  its 
home  more  frequently  in  a  hollow  tree  or  stump  than  in  a  burrow. 

The  genus  Canis  is  represented  in  North  America  by  the  gray 
or  timber  wolf,  C  occidentalism  and  the  coyote,  or  prairie-wolf, 
C.  latrans.  The  gray  wolf  ranges  over  the  Great  Plains  and  the 
Rocky  Moimtains.     It  is  over  four  feet  in  length  and  very  power- 


654 


COLLEGE  ZOOLOGY 


ful.  Wolves  hunt  in  packs,  and  are  able  to  capture  deer  and 
other  large  animals.  They  destroy  great  numbers  of  calves, 
colts,  and  sheep,  and  are  shot,  trapped,  or  poisoned  whenever 
possible.  Many  states  pay  a  high  bounty  for  wolf  scalps.  The 
young,  usually  five  in  number,  are  born  early  in  May. 

Coyotes  are  common  on  the  plains  and  deserts  of  the  West. 
Their  pointed  ears  and  drooping  tails  distinguish  them  easily 
from  dogs.  They  are  fond  of  poultry,  lambs,  and  sheep,  but 
if  these  are  properly  protected,  turn  their  attention  to  rabbits, 

mice,  and  other 
noxious  mammals, 
thereby  becoming 
an  ally  of  the 
farmer. 

The  Procyon- 
iDiE  are  mostly 
confined  to  Amer- 
ica. The  com- 
monest species  is 
the  raccoon,  Pro- 
cyon  lotor  (Fig.  519).  This  form,  as  well  as  the  Texas  bassaris, 
and  the  Mexican  coati,  which  also  occur  in  North  America,  can 
be  recognized  at  once  by  their  black-  and  white-ringed  tail. 
The  raccoon  walks  on  its  entire  foot  (plantigrade),  and  is  about 
two  and  a  half  feet  in  length.  It  prefers  to  live  in  a  hollow 
tree,  and  is  omnivorous.  Its  flesh  is  considered  by  many  people 
an  excellent  article  of  food. 

The  best-known  bears  (Ursid^e)  of  North  America  are  the 
polar  bear,  black  bear,  grizzly  bear,  and  the  large  Alaska  brown 
bear.  They  are  all  plantigrade,  and  have  a  thick,  clumsy  body 
and  rudimentary  tail.  The  polar  bear,  Thalarctos  maritimus, 
frequents  the  coasts  of  the  Arctic  Ocean,  feeding  principally 
upon  seals,  walruses,  and  fish.  The  black,  brown,  or  cinnamon 
bear,  Ursus  americanus,  is  a  smaller  species  abundant  through- 
out the  forested  regions  of  North  America,  where  not  exter- 


FiG.  519. 


The  raccoon,  Procyon  lotor.     (From 
Beddard.) 


CLASS  MAMMALIA 


6SS 


minated.  It  is  omnivorous,  being  especially  fond  of  fish,  blue- 
berries, and  honey.  The  grizzly  bear,  Ursus  horribilis,  of  the 
Rocky  Mountains  is  now  rare  except  in  the  Yellowstone  Park 
and  certain  other  limited  localities. 

The  martens  (Mustelid^)  constitute  a  large  family  of  small 
fur-bearing  animals.  The  best  known  of  the  forty-six  or  more 
species  inhabiting  North  America  north  of  Mexico  are  the  otter, 
mink,  weasel,  marten,  wolverine,  skunk,  and  badger.  The 
otter,  Lutra  canadensis,  is  over  three  feet  in  length.  It  makes 
its  home  in  a  burrow  in  the 
bank  of  a  lake  or  stream  and 
is  very  fond  of  water,  being 
adapted  for  swimming  by 
webbed  feet  and  a  flattened 
tail.  Fish  constitute  its 
chief  food.  Otter  fur  is 
very  valuable,  but  cannot 
be  obtained  now  except  in 
certain  parts  of  Alaska, 
where  the  natives  capture 
the  sea  otter,  Latax  lutris,  a 
single  skin  of  which  is  worth 
in  some  cases  one  thousand 
dollars. 

The  mink,  Putorius  vison,  is  less  than  two  feet  in  length,  and 
dark  brown  in  color.  Lijie  the  otter,  it  is  fond  of  water.  Its 
food  consists  of  birds,  small  mammals,  and  fish.  The  weasel, 
Putorius  noveboracensis,  is  one  of  the  smallest  of  the  Musteltd^. 
It  is  very  bloodthirsty,  often  killing  a  great  many  more  birds 
and  small  mammals  than  it  can  eat.  The  skunks,  Spilogale  and 
Mephitis  (Fig.  520),  are  notorious  because  of  the  powerful  odor 
of  the  secretion  which  they  can  eject  from  a  pair  of  scent  glands 
at  the  base  of  the  tail.  They  feed  upon  poultry,  but  pay  for  their 
board  by  killing  grubs  and  other  noxious  insects.  The  badger, 
Taxidea  taxus,  is  over  two  feet  in  length.     It  inhabits  western 


Fig.  520.  —  The  skunk,  Mephitis  mephitica. 
(From  Flower  and  Lydekker.) 


656  COLLEGE  ZOOLOGY 

North  America,  ranging  east  to  Wisconsin;  lives  in  a  burrow  in 
the  ground;  and  feeds  on  small  mammals.  The  wolverine,  Gulo 
luscus,  is  one  of  the  larger  martens.  It  occurs  in  the  northern 
United  States.  Wolverines  are  fierce,  greedy  animals,  and  great 
thieves,  stealing  bait  from  traps,  and  even  the  traps  themselves. 

The  family  Felid^e  includes  the  cat,  puma,  leopard,  lion,  tiger, 
lynx,  and  cheetah.  The  principal  species  inhabiting  North 
America  are  the  wildcat,  Canada  lynx,  puma,  and  jaguar.  The 
wildcat.  Lynx  ruffus,  also  called  bay  lynx,  bob  cat,  or  catamount, 
is  a  stub-tailed  animal  about  three  feet  in  length,  and  weighs  up 
to  eighteen  pounds.  It  was  formerly  common,  but  is  now  re- 
stricted to  the  forests  of  thinly  settled  localities.  Its  food  con- 
sists of  rabbits,  poultry,  and  other  birds  and  mammals.  The 
Canada  lynx,  or  "  loup  cervier,"  Lynx  canadensis,  is  slightly 
larger  than  the  wildcat,  and  can  be  recognized  by  a  tuft  of  stiff, 
black  hairs  projecting  upward  from  each  ear.  It  occurs  in  the 
northern  United  States  and  in  Canada.  The  puma,  cougar, 
mountain  lion,  or  panther,  Felis  cougar,  reaches  a  length  of  over 
eight  feet,  of  which  the  tail  constitutes  about  three  feet.  Pumas 
make  their  homes  in  rocky  caverns,  or  in  forests.  They  prey 
upon  many  kinds  of  animals,  frequently  causing  much  damage 
by  killing  young  colts;  but  they  do  not  attack  man  unless  cor- 
nered. The  jaguar,  Felis  onca,  is  the  largest  American  cat,  but 
only  occasionally  enters  the  southern  United  States  from  Mexico, 
where  it  is  common.  It  is  spotted  and  has  a  shorter  tail  than 
the  puma.  The  jaguar  is  afraid  of  man,  but  is  a  dangerous  enemy 
of  deer,  horses,  cattle,  and  other  animals. 

The  largest  living  cat  is  the  tiger,  Felis  tigris,  and  related 
species,  whose  body  reaches  a  length  of  ten  feet;  it  is  most  abun- 
dant in  southern  Asia.  The  lion,  Felis  leo,  is  found  in  Africa 
and  certain  parts  of  Asia;  it  is  slightly  smaller  than  the  tiger. 
The  cheetah,  or  hunting  leopard,  Acinonyx  jtihatus,  occurs  in 
parts  of  Asia  and  Africa.  In  India  it  is  trained  to  capture 
game. 

The  aquatic  carnivores  (suborder  Pinnipedia)  are  greatly 


CLASS  MAMMALIA 


657 


modified  for  life  in  the  water.  The  hands  and  feet  are  fully 
webbed,  and  serve  as  swimming  organs,  and  the  body  has  ac- 
quired a  fish-like  form  suitable  for  progress  through  the  water. 
They  are  chiefly  marine,  but  a  fe^  inhabit  fresh  water,  or  swim 
up  rivers.  The  three  families  are  the  eared  seals  (Otariid^), 
the  walruses  (Odob^nid^-),  and  the  earless  seals  (Phocid.'E); 
all  of  them  have  representatives  on  American  shores. 

The  family  Otariid^  includes  the  sea-lions,  fur  seals,  and  sea- 
bears.  The  fur  seal,  Otoes  alascanus,  breeds  on  the  Pribilof 
Islands  in  Bering  Sea,  but  at  other  times  occurs  along  the  coast 
of  California.  Fur  seals  are  polygamous,  and  a  single  old  male 
maintains  control  over  from  six  to  thirty  females.  One  young 
is  produced  each  year.  The  three-year-old  males,  called 
"  bachelors,"  are  the  ones 
killed  for  their  fur.  The 
California  sea-lion,  Zal- 
ophus  calif ornianus ,  is  the 
member  of  this  family  most 
often  seen  in  captivity. 
Squids,  shell-fish,  and  crabs 
are  its  principal  articles  of 
food.  Its  fur  is  short, 
coarse,  and  valueless. 

The  family  Odob^nid^ 
contains  two  living  species, 
the  Atlantic  walrus,  Odo- 
boRuus  rosmarus  (Fig.  521),  and  the  Pacific  walrus,  O.  obesus. 
An  adult  male  walrus  is  ten  or  twelve  feet  long  and  weighs 
almost  a  ton.  The  canine  teeth  of  the  upper  jaw  are  very 
long,  and  are  used  to  dig  up  mollusks  and  crustaceans  from  the 
muddy  bottoms,  and  to  climb  up  on  the  blocks  of  ice  in  the 
Arctic  seas,  where  it  lives.  Walruses  have  been  almost  exter- 
minated for  their  ivory,  skins,  and  oil. 

The  seals  belong  to  the  family  Phocid^.     The  harbor  seal, 
Phoca  vitulina,  inhabits  the  North  Atlantic;    the  ringed  seal, 
2  u 


Fig.    52] 
marus. 


.  —  The   walrus,    Odoboenus   ros- 
(From  Flower  and  Lydekker.) 


658  COLLEGE  ZOOLOGY 

P.  hispida,  and  the  harp  seal,  P.  grosnlandica,  live  in  the  Arctic 
seas;  Pallas'  seal,  P.  largha,  is  the  seal  of  the  North  Pacific. 

Order  Rodentia  (Glires).  —  Gnawing  Mammals. — The 
rodents  are  characterized  by  their  long,  chisel-shaped  incisors 
(Fig.  511,  14,  16),  which  are  adapted  for  gnawing,  and  the  ab- 
sence of  canines,  leaving  a  gap  between  the  incisors  {14)  and  pre- 
molars (75).  They  are  all  small  or  of  moderate  size,  and  num- 
ber over  fourteen  hundred  species,  constituting  the  largest  order 
of  mammals.  South  America  is  richest  in  the  number  of  species. 
The  best-known  North  American  families  are  the  rabbits  and 
hares  (Leporid^),  the  squirrels  (Sciurid^e),  the  beavers  (Cas- 
TORiDiE),  the  pocket-gophers  (Geomyid^),  the  rats,  mice,  etc. 
(MuRiDiE),  and  the  porcupines  (Ccendid^e). 

The  Leporid-E,  or  rabbits  and  hares,  differ  from  most  other 
rodents  in  the  possession  of  a  pair  of  small  incisors  just  behind 
the  pair  of  large  incisors  in  the  upper  jaw.  The  more  common 
American  species  are  the  cottontail,  or  gray  rabbit,  Syhilagus 
floridanus  mallurus,  the  varying  hare,  or  snow-shoe  rabbit, 
S.  americanus,  and  the  jack-rabbit,  S.  campestris. 

The  family  Sciurid^  includes  the  woodchucks,  prairie-dogs, 
tree-squirrels,  chipmunks,  ground-squirrels,  and  flying  squirrels. 
There  are  about  one  hundred  and  seventy  species  and  geographic 
races  in  North  America.  The  common  tree-squirrels  (genus 
Sciurus)  are  the  gray,  fox,  and  red  squirrels;  these  are  all  excel- 
lent climbers,  and  possess  large,  bushy  tails.  They  become 
quite  tame  if  unmolested,  and  with  the  probable  exception  of 
the  red  squirrel  or  chickaree,  should  be  protected. 

The  chipmunks  or  rock  squirrels  (genera  Eutamias  and  Tam- 
ias)  are  small  animals  living  usually  on  the  ground  among  rocks 
(Fig.  522).  The  ground-squirrels  (genera  Citellus,  Callospermo- 
philus,  and  Ammospermophilus)  are  sometimes  called  gophers. 
They  are  inhabitants  of  open  country  and  dig  burrows  in  the 
ground.  Their  food  consists  of  grain  which  they  carry  into 
their  burrows  in  cheek-pouches.  The  prairie-"  dogs  "  (genus 
Cynomys)  are  burrowing  rodents  that  live  on  our  western  plains 


CLASS  MAMMALIA 


659 


in  colonies  of  from  forty  to  one  thousand.  They  feed  upon  grass 
and  other  vegetation.  The  woodchucks,  or  ground-"  hogs " 
(genus  Marmota),  also  live  in  borrows;  but  are  usually  not 
colonial,  and  prefer  hillsides  or  pasture  land  for  their  homes. 
They  feed  on  clover  and  other  grass.  The  flying  squirrels 
(genus  Sciuropterus)  are  delicate  nocturnal  rodents  that  spend 
the  day  asleep  in  a  nest,  usually  in  a  cavity  in  a  tree.  They 
possess  a  thin  fold  of  skin  between  the  fore  and  hind  limbs  on 


Fig.  522.  —  The  chipmunk,  Tamias  striatus.     (From  Ingersoll.) 

either  side,  which,  when  spread  out,  acts  like  a  parachute  to 
sustain  the  animal  in  the  air. 

The  beavers  (CASTORiDiE)  are  the  largest  gnawing  animals  in 
North  America.  They  are  adapted  for  life  in  the  water,  pos- 
sessing webbed  hind  feet  and  a  broad  flat  tail.  The  dams  of 
wood,  grass,  and  mud  made  by  beavers  are  constructed  for  the 
purpose  of  forming  ponds  in  which  houses  are  built  with  under- 
water entrances. 

The  pocket-gophers  (Geomyid^)  possess  large  cheek-pouches, 
which  open  outside  of  the  mouth,  and  strong  fore  feet  provided 


66o 


COLLEGE   ZOOLOGY 


Fig.  523-  ^-  The  pocket  gopher,  Geomys  tuza. 
(From  Davenport,  after  Bailey.) 


with  large  claws  suitable  for  digging  (Fig.   523),     They  occur 
in  the  western  and  southeastern  states,  where  they  burrow  into 

meadows  and  throw 
out  mounds  of 
earth.  Grain  and 
vegetables  are  car- 
ried in  the  pouches 
and  such  quantities 
are  destroyed  as  to 
make  these  rodents 
quite  injurious. 

The  famDy  Murid^  includes  the  muskrats,  lemmings  (Fig. 
524),  meadow-mice,  white-footed  mice,  and  rats.  About  one- 
fourth  of  our  mammals  belong  to  this  family.  They  are  all 
small,  the  muskrat  being  one  of  the  largest  American  species. 
The  common  house  mouse, 
Mus  mus cuius  ^  the  Nor- 
way rat,  Epemys  norvegi- 
cus,  and  black  rat,  E.  rattus, 
have  all  been  introduced 
into  this  country  from  the 
Old  World. 

The  porcupines  (Ccen- 
DiD^)  are  characterized 
by  the  presence  of  spines, 
which  normally  lie  back, 
but  can  be  elevated  by 
muscles  in  the  skin.  The 
Canada  porcupine,  Ere- 
thizon  dorsatus,  ranges 
over  northern  North 
America. 

Order  Edentata.  —  American  Edentates.  —  The  edentates 
are  mainly  inhabitants  of  South  America;  only  one  species,  the 
nine-banded  armadillo,  reaches  the  southern  boundary  of  the 


Fig.  524.  — The  Norwegian  lemming, 
Myodes  lemmus.     (From  IngersoU.) 


CLASS   MAMMALIA 


66 1 


Fig.  525.  — The  great  anteater,  Myrme- 
cophagajubata.  (From  Flower  and  Lydek- 
ker,  after  Sclater.) 


United  States.  They  have  been  grouped  into  three  families: 
the  American  ant-eaters  (Myrmecophagid^),  the  sloths  (Bra- 
DYPODiD^),  and  the  arma- 
dillos (Dasypodid^). 

The  great  ant-eater,  Myr- 
mecophaga  juhata  (Fig.  525), 
measures  about  seven  feet  in 
length,  possesses  a  long,  nar- 
row snout,  and  is  provided 
with  long  claws  on  the  fore 
feet  which  are  used  to  tear 
open  ant-hills.  Its  tongue  is 
long  and  slender  and  serv^es 
to  capture  the  ants  upon 
which  the  animal  feeds. 

The  sloths  inhabit  the  tropical  forests  of  Central  and  South 
America.  They  live  in  the  tree-tops,  and  hang  to  the  underside 
of  the  branches  by  means  of  two  or  three  long,  curved  claws. 
Their  food  consists  of  leaves  and  buds. 

The  armadillos  are  curious  mammals  with  an  armor  of  bony 
scutes.     When  disturbed,  they  roll  up  into  a  ball,  in  which  con- 
dition they  are  not  easily 


injured.  The  nine-banded 
armadillo,  Tatusia  novem- 
cincta  (Fig.  526),  ranges 
from  southern  Texas  to 
Paraguay.  It  is  about 
two  feet  long,  and  lives 
on  the  open  plains,  feeding 
chiefly  upon  worms  and 
insects. 

Order  Phclidota. — S  caly 
Ant-eaters.  —  This  order 
contains  a  single  genus  (Manis)  and  seven  species  of  peculiar 
mammals,  called  pangolins   (Fig.  527),  inhabiting  Africa  and 


Fig.  526.  — The  nine-banded  armadillo, 
Tatusia  novemcincta.  (From  Flower  and 
Lydekker.) 


662 


COLLEGE  ZOOLOGY 


Fig.  527. — The  white-bellied  pan- 
golin, Manis  tricuspis.  (From  Flower 
and  Lydekker.) 


eastern  Asia.     Their  bodies  are  protected  by  overlapping  epi- 
dermal scales  which  can  be  erected.     Like  the  armadillo,  they 

can  roll  themselves  into  a  ball. 
The  tongue  is  long  and  ex- 
tensile; it  is  used  to  capture 
white  ants  or  termites,  upon 
which  it  feeds.  Pangolins  walk 
on  the  dorsal  surface  of  the 
claws  of  the  fore  feet  and  on 
the  soles  of  the  hind  feet.  They 
are  terrestrial,  burrowing,  or 
arboreal,  and  from  one  to  five 
feet  in  length. 

Order  Primates.  —  Lemurs, 
Monkeys,  Apes,  Man. — There 
are  two  suborders  and  eight 
families  of  living  primates;  the 
lemurs  (Lemurid^e),  aye-ayes  (Chiromyid.e),  tarsiers  (Tar- 
siiD.^),  marmosets  (HAPALiDiE),  South  American  monkeys 
(C'ebidm),  Old- World  monkeys  (Cercopithecid^),  anthropoid 
apes  (SiMiiD^),  and  mankind  (Hominid^).  It  is  customary 
to  place  these  animals  at  the  end  of  the  vertebrate  series,  but 
they  excel  the  Ungulata  and  Cetacea  chiefly  in  the  large  size 
of  the  brain,  and  retain  many  primitive  characters,  some  of 
which  are  found  elsewhere  only  among  the  lowest  placental  mam- 
mals, the  Insectivora. 

The  primates  inhabit  chiefly  the  warm  parts  of  the  world. 
They  are  mostly  arboreal  in  habit,  and  are  able  to  climb  about 
among  the  trees  because  the  great  toe  and  thumb  are  oppos- 
able to  the  other  digits,  adapting  the  hands  and  feet  for  grasping. 
A  few  primates  lead  a  solitary  life,  but  most  of  them  go  about  in 
companies.  Fruits,  seeds,  insects,  eggs,  and  birds  are  the  princi- 
pal articles  of  food.  One  young  is  usually  produced  at  a  birth; 
it  is  cared  for  with  great  solicitude. 
The  lemurs  (LEMURiDiE)  are  quadrupeds  and  small  or  moderate 


CLASS   M.\MMALIA 


663 


in  size;  they  are  covered  with 
fur,  and  usually  possess  a  long 
tail  (Fig.  528).  The  face  is 
elongated;  the  brain  case  is 
relatively  small,  and  the  hind 
limbs  are  always  lopger  than 
the  fore  limbs.  The  fifty  liv- 
ing species  are  mostly  confined 
to  Madagascar  and  neighbor- 
ing islands ;  the  rest  inhabit 
Africa  and  the  Oriental  region. 
Lemurs  are  mostly  nocturnal. 
They  feed  on  fruit  and  various 
other  substances,  and  are  all 
arboreal. 

The  marmosets  (Hapalid^, 
Fig.  529),  are  small  arboreal 
primates  ranging  from  Central 
toe  has  a  flat  nail,  but  the  other 


mm 


Mk 


Fig.  529.  —  The  golden  marmoset, 
Midas  chrysoleucas.  (From  Flower 
and  Lydekker.) 


Fig.  528.  —  The  ring-tailed  lemur, 
Lemur  catta.  (From  Flower  and 
Lydekker.) 

America  to  Brazil.  The  great 
digits  bear  claws;  the  tail  and 
ears  are  long;  the  brain  case  is 
large;  the  thumb  is  not  op- 
posable, and  there  is  a  wide 
space  between 'the  nostril  open- 
ings. They  feed  upon  fruit 
and  insects,  and  produce  three 
young  at  a  birth. 

The  Souj:h  American  mon- 
keys (Cebid^e)  are  arboreal  and 
of  small  or  medium  size ;  the 
thumb,  as  well  as  the  great  toe, 
is  opposable;  all  the  digits  pos- 
sess nails  ;  the  tail  is  usually 
long  and  prehensile,  aiding  in 
climbing ;  the  space  between 
the  nostril   openings   is  wide ; 


664 


COLLEGE  ZOOLOGY 


there  is  no  vermiform  appendix.     The  principal  groups  are  the 
howlers,  sakis,'  squirrel  monkeys,  and  spider  monkeys. 

The  howling  monkeys  (genus  Aloudtta)  range  from  South 
America  to  Mexico.  They  possess  a  resonating  apparatus,  with 
which  they  increase  the  power  of  the  howls  they  are  in  the  habit 
of  emitting,  probably  for  the  purpose  of  frightening  away  ene- 
mies. The  sakis  (genus  Pithecia)  inhabit  northern  South  Amer- 
ica ;  they  have  long,  bushy  tails  which  are  non-prehensile.  The 
squirrel  monkeys  (genus  Chrysothrix)  are  very  active  species  in- 
habiting central  and  north- 
ern South  America.  The 
spider  monkeys  (genus 
A  teles,  Fig.  530)  are 
slender,  long-limbed  forms 
ranging  northward  into 
southern  Mexico.  They 
possess  a  very  prehensile 
tail,  but  the  thumb  is 
lacking. 

The  Old  World  monkeys 
(CERCOPiTHECiDiE)  are 
mostly  quadrupedal,  and 
have  hind  limbs  about  as 
long  as  the  fore  limbs. 
They  usually  possess  a  long 
tail,  which  is  never  prehensile;  their  buttocks  are  provided  with 
thick  patches  of  callous  skin  on  which  they  rest  when  in  a  sitting 
posture;  their  nostrils  are  separated  by  a  narrow  space;  and 
many  of  them  have  cheek-pouches.  The  Indian  and  African 
monkeys  belong  to  this  family.  Only  one  species,  the  Barbary 
ape,  enters  Europe;  this  peculiar  tailless  form  is  found  on  the 
Rock  of  Gibraltar. 

The  anthropoid  apes  (Simiid^)  are  the  primates  most  nearly 
related  to  man.  The  tail  is  absent;  the  fore  limbs  are  longer 
than  the  legs;  locomotion  is  often  bipedal,  and  when  walking  the 


Fig.  530.  —  The  black-handed  spider 
monkey,  A  teles  melanochir.  (From  Flower 
and  Lydekker.), 


CLASS  MAMMALIA 


665 


feet  tend  to  turn  in,  and  the 
knuckles  help  preserve  equi- 
librium. There  are  four  genera 
in  the  family:  (i)  Hylobates,  or 
gibbons,  (2)  Pongo  (Simia),  or 
orang-utans,  (3)  Gorilla,  or 
gorillas,  and  (4)  Pan  {Anthro- 
popUhecus),  or  chimpanzees. 

The  gibbons  (Fig.  531)  are  ar- 
boreal; they  have  a  slender  body 
and  limbs ;  are  omnivorous ; 
reach  a  height  of  not  over  three 
feet;  and  when  walking  are  not 
assisted  by  the  hands.  There  are  yig.  531.  — The  dun-colored  gib- 
several  species  inhabiting  south  ^on,  Hylobates  entelloides.  (From 
A    •  J  xi-    17      4.T    J-  Flower  and  Lydekker.) 

eastern  Asia,  and  the  East  Indies. 

There  are  one  or  probably  two  or  more  species  of  orang-utans 
(Fig.  532),  confined  to  Borneo  and  Sumatra.  They  live  prin- 
cipally in  the  tree-tops,  where  they  construct  a  sort  of  nest  for 
themselves.     Orang-utans  are  herbivorous,  about  four  and  a  half 

feet  in  height,  and  when 
w^alking  use  their  knuckles 
as  well  as  their  feet.  The 
brain  of  this  species  is  more 
nearly  like  that  of  man  than 
the  brain  of  any  other 
animal. 

The  gorilla.  Gorilla  gorilla 
(Fig.  533).  inhabits  the 
forests  of  western  Africa. 
It  is  arboreal ;  feeds  mainly 
on  vegetation;  has  large 
canine    teeth  ;     reaches    a 

,J^^-     532. -The      orang-utan,     Pongo    j^^-   j^^    ^f    ^^^    ^^^    ^    ^isM 
(Stmta)  satyrus,  sitting  in  its  nest.     (From  '^ 

Shipley  and  MacBride.)  feet  and  a  weight  of  about 


666 


COLLEGE  ZOOLOGY 


-  ■•\)' 


fiG.  533. — The  gorilla,  Gorilla  gorilla 
(From  Flower  and  Lydekker.) 


five  hundred  pounds;  walks  on 
the  soles  of  its  feet  aided  by 
the  backs  of  the  hands;  and  is 
ferocious  and  untamable. 

The  chimpanzee,  Pan  (An- 
thropopithecus)  troglodytes  (Fig. 
534),  also  lives  in  West  Africa. 
It  resembles  the  gorilla,  but  has 
shorter  arms  and  a  smoother, 
rounder  skull.  In  many  re- 
spects the  chimpanzee  is  more 
nearly  like  man  than  any  other 
living  mammal.  It  is  easily 
tamed. 

The  family  HoMiNiDiE  con- 
tains the  single  living  species, 
Homo  sapiens,  or  man.  Man  differs  from  the  other  primates  in 
the  size  of  the  brain,  which  is  about  twice  as  large  as  that  of 
the  highest  monkey,  and  in  his 
erect,  bipedal  locomotion.  The 
hairy  covering  is  not  well  de- 
veloped, and  the  great  toe  is 
not  opposable.  The  mental  de- 
velopment of  man  has  enabled 
him  to  accommodate  himself  to 
every  climate,  and  to  dominate 
all  other  animals.  Some  fossil 
remains  of  a  primate  that  were 
found  in  the  upper  Pliocene  on 
the  island  of  Java  have  been 
designated  by  Haeckel  as  "  the 
last  link  "  between  the  apes  and 
man,  and  the  animal  to  which  Fig.  534.  —  The  chimpanzee,  Pan 
they  belonged  has  been  given  the   \^nthropopithecus)  troglodytes,  young. 

,  (trom    Flower    ana    Lydekker,    after 

name  Pithecanthropus  erectus.       Wolf.) 


CLASS  MAMMALIA  667 

The  human  race  may  be  divided  into  three  primary  groups 
(Sedgwick) :  (i)  the  Negroid  races,  (2)  the  Mongolian,  and  (3) 
the  Caucasian.  The  Negroid  races  possess  frizzly  hair,  dark 
skin,  a  broad,  flat  nose,  thick  lips,'  prominent  eyes^  and  large 
teeth.  They  are  the  African  Negroes,  the  South  African  Bush- 
men, the  Central  African  and  Philippine  Pygmies,  the  Melane- 
sians,  Tasmanians,  and  Australians. 

The  MongoUan  races  possess  black,  straight  hair,  a  yellow- 
ish skin,  a  broad  face  with  prominent  cheek-bones,  a  small  nose, 
sunken  narrow  eyes,  and  teeth  of  moderate  size.  They  are  the 
inhabitants  of  northern  and  central  Asia,  the  Lapps,  Finns, 
Magyars,  Turks,  Esquimaux,  Malay,  brown  Polynesians,  and 
American  Indians. 

The  Caucasian,  or  white  races,  possess  soft,  straight  hair,  a 
well-developed  beard,  retreating  cheek-bones,  a  narrow  promi- 
nent nose,  and  small  teeth.  There  are  two  main  varieties: 
(i)  the  Xanthochroi,  with  fair,  white  skin,  ranging  from  north- 
ern Europe  into  North  Africa  and  western  Asia;  and  (2)  the 
Melanochroi,  with  black  hair,  and  white  to  black  skin,  inhabit- 
ing southern  Europe,  northern  Africa,  and  southwestern  Asia. 

An  extinct  species  of  man.  Homo  neanderthalensis,  has  b^en 
named  from  remains  found  in  a  limestone  cave  in  the  Neander- 
thal, near  Diisseldorf ,  Germany.  The  skull  is  distinctly  human, 
and  is  the  most  primitive  and  least  specialized  of  any  known. 

Order  Artiodactyla.  —  Even-toed  Hoofed  Mammals.  —  This 
order  contains  the  majority  of  the  "  game  "  animals,  and  in- 
cludes the  pigs  (SuiD^),  peccaries  (Tayassuid^)  ,  hippopotami 
(H1PPOPOTAMID.E) ,  camels  and  llamas  (Camelid^),  chevro- 
tains  (Tragulid^),  giraffes  (Giraffid.e)  ,  deer  (Cervid^e), 
pronghorn  antelopes  (Antilocaprid^),  and  antelopes,  sheep, 
goats,  cattle,  etc.  (Bovid^e).  These  animals  are  characterized 
by  the  presence  of  an  even  number  of  hoofed  toes;  the  axis  of 
symmetry  passes  between  digits  three  and  four.  The  families 
Tayassuid^e,  Cervid^,  Antilocaprid^.  and  Bovid^  are  repre- 
sented in  North  America. 


668 


COLLEGE  ZOOLOGY 


The  term  ruminant  has  been  given  to  the  animals  belonging  to 
the  camel,  chevrotain,  deer,  giraffe,  pronghorn,  and  ox  families, 
since  they  ruminate  or  chew  their  cud.  The  food  of  these  ani- 
mals is  swallowed  without  sufficient  mastication;  it  is  later  re- 
gurgitated in  small  quantities  and  thoroughly  chewed.  This 
method  of  feeding  enables  "  these  comparatively  defenseless  ani- 
mals to  gather  nutriment  in  a  short  time  and  then  retreat  to  a 
safe  place  to  prepare  it  for  digestion."  A  typical  ruminant  pos- 
sesses a  stomach  consisting  of  four  chambers  (Fig.  535):    the 


'^IG.  S3S-  —  Stomach  of  a  ruminant  opened  to  show  internal  structure. 
a,  oesophagus;  b,  rumen;  c,  reticulum;  d,  psalterium;  e,  abomasum;  /,  duo- 
denum.    (From  Flower  and  Lydekker.) 


first  two,  the  rumen  {h)  and  the  reticulum  (c),  belong  to  the 
cardiac  division;  and  the  other  two,  the  psalterium  {d)  and  the 
abomasum  (e),  belong  to  the  pyloric  division.  The  food  is  first 
taken  into  the  rumen  {b),  where  it  is  moistened  and  softened;  it 
passes  back  into  the  mouth  as  "  cuds  "  and  is  ground  up  by  the 
molar  teeth  and  mixed  with  saliva.  When  the  cuds  are  swal- 
lowed, they  are  received  by  the  reticulum  {c) ,  then  pass  into  the 
psalterium  (d),  and  finally  into  the  abomasum  (e). 

The  peccaries  (Tayassuid^e)  are  pig-like  animals  confined  to 
America.  They  possess  large,  prominent  canine  teeth,  and  in- 
cisors in  both  jaws,  but  are  without  horns.  The  Texas  peccary, 
Tayassu  angulatum,  occurs  in  Texas.     It  looks  like  a  small  black 


CLASS  MAMMALIA  669 

pig;  is  nocturnal;  goes  about  in  companies;  and  feeds  on  nuts 
and  roots. 

The  deer  (Cervid^e)  constitute  the  majority  of  the  American 
hoofed  mammals.  Their  horns  or  antlers  are  solid,  and  are  shed 
annually.  The  best-known  species  are  the  wapiti  or  elk,  Vir- 
ginia deer,  mule  deer,  with  round  horns,  and  the  caribou  and 
moose,  with  flat  horns. 

The  moose,  Alces  americanus,  is  the  largest  member  of  the 
family  and  possesses  the  most  massive  antlers.  It  inhabits  the 
woods  of  the  northern  United  States  and  British  America,  and 
feeds  on  bark,  twigs,  leaves,  moss,  and  lichens.  A  larger  and 
darker  race  occurs  in  Alaska.  The  woodland  caribou,  Rangifer 
caribou,  lives  in  the  forested  parts  of  northern  Maine  and  Mon- 
tana, and  British  America.  The  female  caribou  is  our  only 
female  deer  that  bears  antlers.  The  reindeer  also  belongs  to  the 
genus  Rangifer. 

The  wapiti  or  elk,  Cervus  canadensis,  is  the  largest  round- 
horned  deer.  It  is  easily  bred  in  confinement,  and  is  common 
in  zoological  parks.  The  Virginia  or  white-tailed  deer,  Odocoi- 
leus  virginianus,  is  the  best  known  and  most  widely  distributed 
of  all  our  species.  It  is  an  inhabitant  of  forests.  The  mule 
deer  or  black-tailed  deer,  Odocoileus  hemionus,  is  a  large,  high- 
headed  species,  which  prefers  open  country.  It  browses  on 
twigs  and  leaves,  and  also  grazes  when  the  grass  is  good.  Two 
fawns  are  usually  produced  at  a  birth. 

The  pronghorn  antelopes  (Antilocaprid^)  are  confined 
to  the  open  country  of  western  North  America.  Their  horns 
are  hollow,  branched,  and  shed  annually.  There  is  but  a  single 
species,  Antilocapra  americana. 

The  family  Bovid.^  contains  the  gnus,  hartebeests,  dik-diks, 
waterbucks,  gazelles,  elands,  chamois,  Rocky  Mountain  goats, 
sheep,  goats,  musk-oxen,  oxen,  and  bison.  These  are  all  rumi- 
nants (see  p.  668),  and  both  males  and  females  usually  possess 
unbranched,  hollow  horns,  which  fit  over  bony  prominences  on 
the  skull  and  are  not  shed  annually.     The  best-known  Ameri- 


670 


COLLEGE  ZOOLOGY 


can   forms  are   the    bison,   musk-ox,   bighorn,   and    mountain 
goat. 

The  bison,  Bison  bison  (Fig.  536),  up  to  the  year  1870,  ranged 
over  a  large  part  of  the  Great  Plains  and  other  portions  of  North 
America.  It  was  persistently  hunted  chiefly  for  its  hide  until 
most  of  the  species  had  been  killed.  In  1903  it  was  estimated 
that  about  six  hundred  wild  individuals  and  one  thousand  cap- 
tive specimens  still  existed.     The  musk-ox,  Ovibos  moschatus 


Fig.  536.  — The  American  bison,  Bison  bison.     (From  Beddard.) 


(Fig.  537),  lives  on  the  Arctic  barrens  of  North  America.  It  has 
a  long,  shaggy  coat,  and  the  male  has  a  strong,  musky  smell. 
The  Esquimaux  use  it  for  many  purposes.  The  bighorn,  or 
mountain  sheep,  Ovis  cervina,  is  an  inhabitant  of  the  slopes  of  the 
Rocky  and  Sierra  mountains  above  timber  line.  It  seeks  the 
more  sheltered  valleys  in  the  winter.  The  mountain  goat, 
Oreamnos  montanus,  occurs  in  the  higher  Rocky  and  Cascade 
mountains  to  Alaska.  It  is  covered  with  long,  white  hair;  has 
slender  black  horns;   and  is  an  expert  climber. 

Among  the  Artiodactyla  not  found  in  North  America  are: 


CLASS  MAMMALIA 


671 


(i)  the  wild  boar,  Sus  scrofa,  of  Europe;  (2)  the  wart  hog,  Phaco- 
chcerus  cethiopicus,  of  Africa;  (3)  the  hippopotamus,  Hippopota- 
mus amphibius,  of  Africa;  (4)  thexamel,  Camelus  bactrianus,  of 
Asia;  (5)  the  dromedary,  Camelus  dromedarius,  of  Arabia;  (6)  the 
llama.  Lama  glama,  of  South 
America;  (7)  the  chevro tains, 
Tragulus  and  HycBmoschus,  of 
India,  Malay,  and  Africa,  among 
the  smallest  living  ruminants; 
(8)  the  okapi,  Ocapia  johnstoni, 
of  the  Congo;  (9)  the  giraffe, 
Girafa  camelopardalis,  of  Africa; 
(10)  the  gazelles,  Gazella,  of 
Africa  and  Asia;  (11)  the  cham- 
ois,    Rupicapra,     of     southern       Fig.  537.  -  The  musk-ox    Ovibos 

moschatus.    (From  Flower  and  Lydek- 

Europe  and  southwestern  Asia;   ter.) 

(12)  the  buffaloes,   Bubalus,  of 

Africa  and  Asia;  and  (13)  the  yak,  Poephagus,  of  the  Himalayas 

and  Thibet. 

Order  Perissodactyla.  —  Odd-toed  Hoofed  Mammals.  — 
The  horses  (Equid^e),  tapirs  (Tapirid^),  and  rhinoceroses 
(Rhino CEROTiD^)  belong  to  this  order.  They  are  characterized 
by  the  presence  of  an  odd  number  of  hoofed  toes;  the  axis  of 
symmetry  passes  through  the  third  digit.  None  of  the  Perisso- 
dactyla are  native  to  the  United  States,  but  many  remains  of 
extinct  species  have  been  found. 

The  horses,  zebras,  and  asses  of  the  family  Equid.'E  have  but 
one  functional  toe  on  each  foot,  and  two  lateral  splints.  The 
common  horse,  Equus  caballus,  of  which  over  sixty  domesticated 
races  exist,  is  not  now  known  in  a  wild  state.  There  are  several 
species  of  wild  asses  in  Asia  and  Africa.  The  Nubian  ass,  Equus 
africanus,  is  probably  the  parent  of  the  domestic  donkey.  The 
zebras  are  confined  to  Africa,  and  may  be  divided  into  several 
specific  types  with  numerous  subspecies.  The  common  zebra 
is  Equus  zebra. 


672 


COLLEGE   ZOOLOGY 


The  tapirs  (Tapirid^)  have  four  toes  on  the  fore  feet  and  three 
on  the  hind  feet.  They  occur  in  Central  and  South  America, 
Sumatra,  Java,  and  the  Malay  Peninsula.  The  American  tapirs 
(Fig.  538)  have  a  long,  prehensile  nose.  They  feed  on  soft 
plants  and  are  hunted  for  their  flesh. 

The  rhinoceroses  are  large,  thick-skinned  mammals  with  one 
or  two  epidermal  horns  on  the  nasal  and  frontal  bones.     The 


Fig.  538.  —  The  American  tapir,  Fig.  539.  —  The  Indian  rhinoceros, 

Tapirus  americanus.     (From  Flower         Rhinoceros  unicornis.     (From  Flower 
and  Lydekker.)  and  Lydekker,  after  Wolf.) 

Indian  species  (Fig.  539)  has  one  horn;  the  Sumatran  form  has 
two,  as  has  also  the  white  rhinoceros  of  Africa. 

Order  Proboscidea.  —  Elephants.  —  There  are  two  genera  of 
elephants,  each  with  one  living  species.  The  Asiatic  elephant, 
Elephas  indicus,  inhabits  the  jungles  of  India;  the  African  ele- 
phant, Loxodonta  africanus  (Fig.  540) ,  lives  in  tropical  forests 
and  is  hunted  for  its  tusks.  Both  species  possess  five  digits  on 
each  foot;  are  covered  by  a  thick,  loose  skin  (therefore  called 
pachyderms)  with  a  thin  coat  of  hair;  have  a  long,  muscular 
proboscis  with  nasal  openings  at  the  tip;  are  provided  with  tusks 
which  develop  from  the  incisors;  possess  small  eyes  and  tail 
and  enormous  ears;  and  are  without  canine  teeth.  The  skull 
is  massive,  because  the  bones  are  thickened  and  contain  air 
spaces,  and  the  grinding  teeth  are  very  large  and  possess  com- 
plicated ridges. 


CLASS  MAMMALIA 


673 


^ 

\4 

^ 

s 

i 

m 

'M! 

•^    «. 

^- 1 

^ 
1 

I 

% 

.^1H 

m^B& 

-..     ■ 

1 

SL^r 

Si^:-.^:i'^i^ 

^ 

^^^&|^ 

^^B 

fe_ 

-*:     ^S»^ 

i:^-  J 

*?^ 

Fig.  540.  —  The  African  elephant,  Loxodonta  ajricanus. 
after  Baker.) 


(From  Beddard, 


Order  Sirenia.  —  Sea-cows.  — This  order  contains  four  species 
of  manatees  (genus  Manatus) ,  one  on  the  Atlantic  coast  of  Africa, 
and  three  on  the  Atlantic  coast  of  America;  and  three  species 
of  dugongs  (genus  Dugong)  on  the  shores  of  the  Red  Sea,  Indian 
Ocean,  and  Australia. 

Steller's  sea-cow  (Rhytina)  formerly  inhabited  the  north 
Pacific,  but  became  extinct  about  1768  because  its  fearlessness 
enabled  hunters  to  kill  it 
easily.  Sea-cows  differ  con- 
siderably in  structure  from 
whales.  Their  bones  are 
heavy,  enabling  them  to 
remain  on  the  bottom;  the 
teeth  are  broad  and  crush- 
ing; the  lips  are  large  and 
movable  and  are  used  to  seize  seaweeds  and  other  water-plants 
upon  which  they  feed  ;    the  fore  Hmbs  are  flexible   flippers ; 


Fig.  541.  —  The 
Manatus  laiirostris. 
Lydekker.) 


American     manatee, 
(From    Flower    and 


674  COLLEGE  ZOOLOGY 

and  the  tail  is  rounded  and  not  notched  as  in  whales.  The 
Florida  manatee,  Manatus  latirostris  (Fig.  541),  is  about  nine 
feet  in  length.     It  is  now  nearly  extinct. 

Order  Odontoceti  (Denticeti).  —  Toothed  Whales.  —  Four 
families  belong  to  this  order:   (i)  the  Platanistid^,  or  river 


Fig.  542.  —  The  dolphin,  Dclphinus  delphis.     (From  Sedgwick's  Zoology, 
after  regne  animal.) 

dolphins;  (2)  the  DELPHiNiDiE,  or  dolphins,  porpoises,  gram- 
puses, and  killer  whales;  (3)  the  DELPHiNAPTERiDiE,  or  belugas 
and  narwhales;  and  (4)  the  Physeterid^,  or  sperm  whales  and 
beaked  whales. 

Whales  are  adapted  to  life  in  the  water.     They  possess  a  very 
large  head  with  elongated  face  and  jaw  bones;  the  fore  limbs  are 


Fig.  543.  —  Skull  of  Greenland  whale,  Balcena  mysticelus,  with  the  whale- 
bone.    (From  Sedgwick's  Zoology,  after  regne  animal.) 

modified  as  paddles;  the  tail  is  flattened  horizontally  and  forms 
two  lobes,  the  "  flukes  ";  the  eyes  are  small,  and  there  is  no  exter- 
nal ear.    The  nostrils  form  a  single  semilunar  opening,  and  the 


CLASS  MAMMALIA  675 

air,  which  is  forced  from  it,  condenses  in  the  cold  atmosphere, 
appearing  like  a  spout  of  water.  Beneath  the  skin  is  a  thick 
layer  of  fat,  or  ''  blubber,"  which 'retains  the  body  heat.  The 
teeth  are  numerous,  and  conical  in  shape. 

The  common  dolphin,  Delphinus  delphis  (Fig.  542),  is  about 
seven  feet  in  length;  it  is  common  in  the  Mediterranean,  along 
the  western  coast  of  Europe,  and  in  the  warmer  portions  of  the 
Atlantic.  The  sperm-whale,  Physeter  macrocephalus  (Fig.  544), 
reaches  a  length  of  seventy-five  feet,  and  is  the  largest  toothed 
whale.  Its  oil,  spermaceti,  and  blubber  are  sought  by  whalers. 
Cephalopods  (p.   264)   are  its  principal  food.     The  narwhale, 


Fig.  544.  —  The  sperm  whale,  Physeter  macrocephalus.     (From  Flower 
and  Lydekker.) 

Monodon  monoceras,  inhabits  Arctic  seas;  one  of  its  upper  teeth 
is  a  horizontal,  twisted  tusk  about  five  feet  in  length.  The  killer- 
whale,  Orca  orca,  occurs  in  all  oceans,  is  about  twenty  feet  in 
length,  and,  as  its  name  implies,  is  a  fierce  predatory  mammal, 
killing  fish,  seals,  and  other  whales. 

Order  Mystacoceti. — Whalebone  Whales. — The  single 
family  (Bal^enid^)  of  whalebone  whales  includes  the  gray 
whale,  Rhacianectes  glaucus,  of  the  North  Pacific,  the  rorqual  and 
fin-whales  (Balosnoptera),  the  hump-backed  whale,  Megaptera 
hoops,  of  the  Atlantic  and  Pacific,  and  the  right  whales  {Baloena). 
These  whales  possess  teeth  only  in  the  embryo;  they  are  pro- 
vided in  the  adult  stage  with  numerous  plates  of  baleen  or  whale- 
bone, which  are  horny  and  frayed  out  at  the  end  (Fig.  543).  In 
feeding  the  whale  takes  large  quantities  of  water  into  its 
mouth,  and  then  forces  it  out  through  the  sieve-like  whalebone, 


676  COLLEGE  ZOOLOGY 

retaining  any  small  organisms  that  may  have  entered  with  the 
water. 

The  sulphur-bottom  whale,  Balcenoptera  sulfureus,  is  the 
largest  whale,  and  the  largest  living  animal,  reaching  a  length 
of  ninety- five  feet,  and  a  weight  of  about  294,000  pounds;  it 
inhabits  the  Pacific  from  California  to  Central  America.  The 
Greenland  whale  or  bow-head,  Baloena  mysticetus,  occurs  in 
polar  seas;  and  reaches  a  length  of  about  sixty  feet.  It  yields 
nearly  three  hundred  barrels  of  oil,  and  about  three  thousand 
pounds  of  the  best  whalebone.  Balcenoptera  musculus  is  a 
sulphur-bottom  whale  occurring  in  the  Atlantic  and  caught  off 
the  coast  of  Newfoundland. 

4.  General  Remarks  on  the  Mammalia 
a.  Integumentary  Structures 

Hair.  —  The  hairs  that  distinguish  mammals  from  all  other 
animals  are  related  phylogenetically  to  the  feathers  of  birds  and 
the  scales  of  reptiles.  They  are  cornified  modifications  of  the 
epidermis  (p.  403,  Fig.  347,  Se.  SM)  which  project  out  from  pits 
in  the  skin,  called  hair  follicles.  The  hair  shaft  ( H)  broadens  at 
the  base,  extending  around  a  highly  vascular  papilla  at  the  bot- 
tom of  the  pit.  When  hairs  are  shed,  new  hairs  usually  arise  to 
take  their  place.  Secretions  from  the  sebaceous  glands  (D)  keep 
the  hairs  glossy. 

The  two  main  types  of  hairs  are  (i)  contour  hairs  which  are 
long  and  strong,  and  (2)  woolly  hairs  which  are  shorter  and  con- 
stitute the  under  fur.  In  some  animals  the  woolly  hairs  have 
a  rough  surface,  as  in  the  sheep,  which  causes  them  to  cohere  and 
gives  them  their  felting  quality.  Certain  of  the  stronger  hairs 
may  be  moved  by  muscular  fibers.  The  muscles  of  the  dermis 
are  responsible  for  the  erection  of  spines  or  the  bristling  of  the 
other  hairs. 

Scales.  —  Scales  are  present  on  the  bodies  of  a  few  mammals, 
notably  in  the  pangolin  (Fig.  527)  and  on  the  tail  of  certain 
rodents,  such  as  the  beaver,  rats,  and  mice. 


CLASS  MAMMALIA 


677 


Claws,  Nails,  Hoofs,  etc.  —  The  claws  of  the  Unguiculata, 
the  nails  of  the  Primates,  and  the  hoofs  of  the  Ungulata  are 
all  modifications  of  the  horny  covering  on  the  dorsal  surface  of 
the  distal  ends  of  the  digits.  Tlie  chief  forms  are  shown  in 
Figure  545.  When  on  the  ground  the  foot  rests  partially  or 
entirely  upon  the  pads  or  tori  (b).     Dermal  papillae  occur  on  the 


1.-5 


Fig.  545.  —  Diagrammatic  longitudinal  sections  through  the  distal  ends 
of  the  digits  of  mammals.  A,  spiny  anteater,  Echidna.  B,  an  unguiculate. 
C,  man.  D,  horse.  1-3,  phalanges;  b,  torus;  N,  nail-plate;  S,  sole-horn; 
W,  bed  of  claw  or  nail.     (From  Wiedersheim,  after  Gegenbaur  and  Boas.) 


tori,  often  forming  concentric  lines  such  as  those  that  produce 
the  finger-prints  of  man.  The  sole-horn  (S)  is  softer  than  the 
nail-plate  (N). 

Other  epidermal  horny  thickenings  are  the  horn-sheaths  of  the 
ox  and  other  ruminants,  the  nasal  horns  of  the  rhinoceros,  and 
the  "  whalebone  "  (baleen,  Fig.  543)  of  certain  whales.  Dermal 
plates  of  bone  form  the  exoskeleton  of  the  armadillos  (Fig.  526). 

Cutaneous  Glands.  —  Mammals  possess  a  greater  number  of 
glands  than  reptiles  or  birds;  these  are  for  the  most  part  seba- 
ceous and  sweat-glands,  or  modifications  of  them.  The  sebaceous 
glands  usually  open  into  the  hair-follicles  (p.  403,  Fig.  347,  D), 


678 


COLLEGE  ZOOLOGY 


and  secrete  a  greasy  substance  which  keeps  the  surface  soft  and 
the  hair  glossy.  The  sweat-glands  (Fig.  347,  SD)  secrete  a  fluid 
composed  chiefly  of  water  containing  a  small  amount  of  solid 
matter  in  solution;  this  fluid  evaporates,  thereby  cooling  the 
skin  and  regulating  the  bodily  temperature.  The  lachrymal 
glands,  whose  secretions  keep  the  eyeballs  moist,  the  scent  glands 

of    many    mammals,    and    the 
Jw         ^  M        mammary  glands,  are  all   modi- 

JV         f^         ^^       fications  of  cutaneous  glands. 


JTi 


Fig.  546.  —  Diagrammatic  section 
of  various  forms  of  teeth.  I,  incisor 
or  tusk  of  elephant  with  pulp  cavity 
open  at  base.  II,  human  incisor, 
during  development,  with  pulp  cav- 
ity open  at  base.  Ill,  completely 
formed  human  incisor,  opening  of 
pulp  cavity  small.  IV,  human 
molar  with  broad  crown  and  two 
roots.  V,  molar  of  ox,  enamel 
deeply  folded  and  depressions  filled 
with  cement.  Enamel,  black;  pulp, 
white ;  dentine,  horizontal  lines ; 
cement,  dots.  (From  Flower  and 
Lydekker.) 


h.  The  Teeth  of  Mammals 

The  teeth  of  mammals  are  of 
considerable  value  in  classifica- 
tion, and  indicate  also  the  food 
habits  of  their  possessors.  Most 
mammals  are  provided  with 
teeth,  but  the  whalebone  whales, 
the  monotremes,  and  many  eden- 
tates are  without  them  in  the 
adult  stage,  and  in  some  forms 
{e.g.  the  spiny  anteater,  Echidna) 
they  have  never  been  found  even 
in  the  embryo. 

The  teeth  are  embedded  in 
sockets  in  the  bone,  but  arise  in- 
dependently of  the  endoskeleton, 
taking  their  origin  from  calci- 
fications of  the  mucous  mem- 
brane of  the  mouth.  The  prin- 
cipal forms  of  teeth  and  the 
relations  of  the  three  constituents 
are  shown  in  Figure  546.  The 
enamel  (in  black)  is  the  outer 
hard  substance  ;  the  dentine 
(horizontal  lines)  constitutes  the 


CLASS  MAMMALL\  679 

largest  portion  of  the  tooth;  and  the  cement  (dotted)  usually 
covers  the  part  of  the  tooth  embedded  in  the  tissues  of  the  jaw. 
The  central  pulp-cavity  of  the  tooth  contains  nerves,  blood- 
vessels, and  connective  tissue.  Teeth  have  an  open  pulp-cavity 
during  growth  (Fig.  546,  II),  which  in  some  cases  continues 
throughout  life  (Fig.  546,  I). 

The  teeth  of  fishes,  reptiles,  and  amphibians  are,  with  few 
exceptions,  all  similar,  and  the  dentition  of  these  animals  is 
therefore  said  to  be  homodont.  The  dentition  of  mammals,  on 
the  other  hand,  is  almost  always  heterodont,  there  being  usually 
four  kinds  of  teeth  in  each  jaw:  (i)  the  chisel-shaped  incisors  in 
front  (Fig.  518,  i  2),  (2)  the  conical  canines  (c),  (3)  the  anterior 
grinding  teeth  or  premolars  (pm  i  —  pm  4),  and  (4)  the  posterior 
grinding  teeth  or  molars  (m  i). 

In  most  mammals  the  first  set  of  teeth,  known  as  the  milk 
dentition,  is  pushed  out  by  the  permanent  teeth,  which  last 
throughout  the  life  of  the  animals.  The  milk  molars  are  fol- 
lowed by  the  premolars,  but  the  permanent  molars  have  no  pred- 
ecessors. 

It  is  customary  to  indicate  the  number  of  each  kind  of  teeth 
possessed  by  a  mammal  by  a  formula  expressed  in  the  form  of  a 
fraction,  of  which  the  numerator  refers  to  those  in  one  half  of 
the  upper  jaw,  and  the  denominator  to  those  in  one  half  of  the 
lower  jaw.  For  example,  the  dog  (Fig.  518)  possesses  three  in- 
cisors (i),  one  canine  (c),  four  premolars  (pm),  and  two  molars 
(m)  in  one  half  of  the  upper  jaw,  and  three  incisors,  one  canine, 
four  premolars,  and  three  molars  in  one  half  of  the  lower 
jaw.     The   dental   formula   of   the    dog   is   therefore   written 

i'  ^',  c  •  -;  pm  •  - ;  w  - ,  or  in  simpler  form  ^ The 

31  4  3  3-I-4-3 

total  number  of  teeth  in  the  dog  may  be  learned  by  adding  these 

numbers  and  multiplying  by  two. 

The  relation  of  the  form  of  the  teeth  to  the  food  habits  of  the 

animal  may  be  shown  by  the  following  examples.     The  dolphins 

(Fig.  542)  have  a  large  number  of  sharp  conical  teeth  adapted 


68o  -COLLEGE  ZOOLOGY 

for  capturing  fish  (compare  teeth  of  perch,  p.  437);  the  carniv- 
orous animals,  Hke  the  dog  (Fig.  518),  are  provided  with  large 
canine  teeth  for  capturing  and  killing  their  prey,  small  and  almost 
useless  incisors,  and  molars  with  sharp  edges  for  cutting  or  crush- 
ing; herbivorous  animals,  like  the  ox,  possess  broad  incisors  for 
biting  off  vegetation,  no  canines,  and  large  grinding  molars 
(Fig.  546,  V);  rodents,  like  the  rabbit  (Fig.  511),  have  incisors 
that  grow  throughout  life,  but  are  worn  down  by  gnawing,  thereby 
maintaining  a  serviceable  length  and  a  keen  cutting  edge;  in- 
sectivores,  such  as  the  shrew  (Fig.  516),  seize  insects  with  their 
projecting  incisors  and  cut  them  into  pieces  with  the  pointed 
cusps  on  their  premolars  and  molars;  and  man  and  other  omniv- 
orous animals  are  provided  with  teeth  fitted  for  masticating 
both  animal  and  vegetable  matter. 

c.    The  Development  of  Mammals 

The  eggs  of  most  mammals  develop  within  the  body  of  the 
mother;  the  exceptions  are  the  monotremes  (p.  645),  which  lay 
eggs.  During  their  development  the  eggs  of  mammals,  as  well 
as  those  of  birds  and  reptiles,  produce  two  membranes:  (i)  the 
amnion,  and  (2)  the  allantois.  Because  of  the  presence  of  these 
membranes,  the  mammals,  birds,  and  reptiles  are  often  grouped 
together  as  Amniota,  while  the  amphibians,  fishes,  elasmo- 
branchs,  and  cyclostomes,  which  do  not  possess  these  mem- 
branes, are  designated  as  Anamniota. 

The  segmentation  of  mammals'  eggs  is  complete  (except  in 
monotremes),  and  takes  place  either  in  the  oviduct,  as  in  the 
rabbit,  or  in  the  uterus,  as  in  the  sheep.  Figure  547  illustrates 
by  a  series  of  diagrams  the  formation  of  the  embryonic  mem- 
branes of  a  mammal.  The  processes  are  briefly  noted  beneath 
the  diagrams. 

The  placenta  which  is  present  in  some  marsupials  and  all  the 
other  EuTHERiA  arises  in  the  following  manner.  "  In  the  uterus 
the  embryo  becomes  connected  with  the  uterine  wall  by  means 
of   its  outer  epithelial   layer,  now  known  as  the  trophoUast, 


Fig.  547.  —  Diagrammatic  figures  illustrating  the  formation  of  the  foetal 
membranes  of  a  mammal,  a,  embryo  before  appearance  of  amnion;  b,  embryo 
with  yolk-sac  and  developing  amnion;  c,  embryo  with  amnion  closing  and 
developing  allantois;  d,  embryo  with  villous  subzonal  membrane,  and  with 
mouth  and  anus;  e,  embryo  in  which  vascular  layer  of  allantois  is  applied  to 
subzonal  membrane,  and  has  grown  into  the  villi  of  the  latter,  yolk-sac 
reduced,  amniotic  cavity  increasing.  A,  embryonic  thickening  of  external 
layer;  Ah,  amniotic  cavity;  Al,  allantoic  stalk;  Am,  amnion;  Ch,  chorion; 
Chz,  chorionic  villi;  D,  D',  zona  radiata;  Dg,  umbilical  stalk;  Dh,  intestinal 
cavity;  Ds,  cavity  of  embryonic  (blastodermic  vesicle),  later  of  the  yolk- 
sac  (umbilical  vesicle);  E,  embryo;  /,  embryonic  thickening  of  inner  layer; 
M,  of  middle  layer;  Sh,  subzonal  membrane  (serous  envelope);  Sz,  villi  of 
subzonal  membrane.     (From  Sedgwick's  Zoology,  after  Kolliker.) 

681 


682  COLLEGE   ZOOLOGY 

This,  later,  becomes  coated  wholly  or  in  part  on  its  inner  side 
by  somatic  mesoblast,  and  constitutes  the  membrane  known  as 
the  subzonal  membrane.  .  .  .  Later  on,  the  mesoblast  of  the 
peripheral  part  of  the  allantois  becomes  applied  to  the  subzonal 
membrane  and  the  two  structures  constitute  the  embryonic 
membrane  called  the  chorion.  .  .  .  The  chorion  develops  vas- 
cular villi  which  enter  into  close  relation  with  the  uterine  wall. 
In  this  manner  there  is  developed  a  relatively  large  surface, 
permeated  with  branches  from  the  foetal  vessels,  the  blood  of 
which  is  in  intimate  osmotic  connection  with  the  blood  of  the 
uterine  wall.  This  connection  of  the  chorion  of  the  foetus  with 
the  uterine  walls  gives  rise  to  the  placenta,  by  means  of  which 
the  nourishment  and  respiration  of  the  foetus  are  provided  for 
in  the  body  of  the  mother.  .  .  .  The  placenta  presents  great 
variations,  in  the  individual  orders,  in  its  special  development 
and  in  the  mode  of  its  connection  with  the  uterine  walls." 
(Sedgwick.) 

d.    Hibernation 

The  problem  of  maintaining  life  during  the  winter  is  solved 
by  most  birds  by  migrating.  Mammals,  on  the  other,  hand, 
usually  remain  active,  like  the  rabbit,  or  hibernate.  During 
hibernation  the  temperature  of  the  body  decreases  and  the  ani- 
mal falls  into  a  profound  torpor.  A  cold-blooded  animal,  like 
the  frog,  can  be  almost  entirely  frozen  without  being  injured, 
but  warm-blooded  animals  must  protect  themselves  from  the 
cold;  they  therefore  seek  a  sheltered  spot,  such  as  a  burrow  in 
the  ground,  in  which  to  spend  the  winter.  Furthermore,  at  this 
time  the  fur  of  mammals  is  very  thick  and  consequently  helps 
to  retain  the  body  heat. 

The  temperature  of  the  body  of  hibernating  animals  becomes 
considerably  lower  than  normal;  for  example,  a  ground  squirrel 
which  hibernated  in  a  temperature  of  35.6°  F.  had  a  body 
temperature  exactly  the  same.  (Semper.)  Respiration  almost 
ceases;   the  heart  beats  very  slowly;    and  no  food  is  taken  into 


CLASS  MAMMALIA 


683 


the  body,  but  the  fat  masses  stored  up  in  the  autumn  are  con- 
sumed, and  the  animal  awakens  in  the  spring  in  an  emaciated 
condition.  , 

The  woodchuck  is  the  most  profound  sleeper  of  our  common 
mammals;  it  feeds  on  red  clover  in  the  autumn,  goes  into  its 
burrow  about  October  i,  and  does  not  come  out  until  April  i. 
The  bear  does  not  sleep  so  profoundly,  for  if  there  is  plenty  of 
food  and  the  temperature  is  mild,  he  will  not  hibernate  at  all. 
When  the  bear  does  hibernate,  he  scoops  out  a  den  under  a  log 
or  among  the  roots  of  a  hollow  tree.  The  raccoon  and  gray 
squirrel  sleep  during  the  severest  part  of  the  winter;  the  skunk 
spends  January  and  February  in  his  hole;  the  chipmiink  wakes 
up  occasionally  to  feed  ;  and  the  red  squirrel  is  abroad  practically 
all  winter.     Many  other  mammals  hibernate  for  a  greater  or  less 

period  of  time. 

e.   Migration 

Comparatively  few  mammals  migrate;  this  may  be  due  in 
part  to  their  inadequate  means  of  locomotion.  Among  those 
that  do  migrate  are  the  fur-seal,  reindeer,  bison,  bat,  and  lem- 
ming. The  fur-seals  in  American  waters  breed  on  the  Pribilof 
Islands  in  Bering  Sea,  where  they  remain  from  about  May  i  to 
September  15.  They  then  put  out  to  sea,  spending  the  winter 
months  making  a  circuit  of  about  six  thousand  miles. 

The  reindeer  of  Spitzbergen  migrate  regularly  to  the  central 
portion  of  the  island  in  summer  and  back  to  the  sea-coast  in  the 
autumn,  where  they  feed  upon  seaweed.  The  bisons  used  to 
range  over  a  large  part  of  North  America,  making  regular  spring 
and  fall  migrations;  they  covered  an  area  of  about  thirty-six 
hundred  miles  from  north  to  south,  and  two  thousand  miles  from 
east  to  west. 

The  lemmings  of  Scandinavia  (Fig.  524)  are  celebrated  for 
their  curious  migrations.  They  are  small  rodents  about  three 
inches  in  length. 

"  At  intervals,  averaging  about  a  dozen  years  apart,  lemmings 
suddenly  appear  in  cultivated  districts  in  central  Norw^ay  and 


684  COLLEGE  ZOOLOGY 

Sweden,  where  ordinarily  none  live,  and  in  a  year  or  two  multiply 
into  hordes  which  go  traveling  straight  west  toward  the  Atlantic, 
or  east  toward  the  Gulf  of  Bothnia,  as  the  case  may  be,  regard- 
less of  how  the  valleys  trend,  climbing  a  mountain  instead  of 
going  around  it,  and,  undeterred  by  any  river  or  lake,  keep  per- 
sistently onward  until  finally  some  survivors  reach  the  sea,  into 
which  they  plunge  and  perish."  They  are  said  to  march  in 
"  parallel  lines  three  feet  apart "  and  "  gnaw  through  hay  and 
corn  stacks  rather  than  go  round."  (Pennant.) 

/.   Domesticated  Mammals 

The  most  common  domesticated  mammals  are  the  dog,  horse, 
ass,  ox,  sheep,  goat,  pig,  and  cat.  The  dog  was  probably  the 
first  mammal  to  be  domesticated.  Dogs  have  been  the  com- 
panions of  man  for  many  centuries;  they  have  become  changed 
while  under  domestication,  until  there  are  now  more  than  two 
hundred  breeds.  In  many  cases  local  wild  species  of  the  genus 
Canis  have  been  tamed;  for  example,  the  original  Arctic  sledge 
dogs  were  half-tamed  gray  wolves,  and  the  dogs  kept  by  our 
northwestern  Indians  were  tamed  coyotes. 

The  immediate  ancestors  of  the  horse  are  not  known,  and  there 
are  at  the  present  time  no  wild  horses  from  which  it  could  have 
arisen.  It  has  probably  developed  from  animals  inhabiting  the 
semiarid  plains  of  central  Asia.  The  more  remote  ancestors 
of  the  horse  are  well  known  (see  Chap.  XXII). 

The  ass  is  the  favorite  beast  of  burden  in  Eastern  countries. 
In  this  country  the  cross  between  a  female  horse  and  male  ass  is 
known  as  a  mule.  The  common  ass  of  Europe  and  America  is 
descended,  through  the  early  Egyptian  domestication,  from 
the  African  wild  ass,  Equus  africanus. 

The  oxen  of  Europe  and  America  were  probably  derived  from 
the  aurochs,  Bos  primigenius,  of  Europe.  The  sacred  or  humped 
cattle  of  India,  Bos  indicus,  doubtless  developed  from  one  of 
the  wild  races  that  still  roam  the  Himalayan  foot-hills. 

Sheep  have  been  doniesticated  for  so  many  centuries  that  their 


CLASS  MAMMALIA  685 

ancestors  are  not  known,  but  there  are  many  wild  sheep  of 
the  same  genus  (Ovis)  from  which  they  may  have  originated. 
Goats  have  also  been  domesticated  since  the  earliest  times, 
and  their  wild  relatives  are  abundant  in  many  parts  of  the 
world. 

The  domesticated  pigs  are  descended  from  the  European  wild 
boar,  Stis  scrofa,  and  the  Indian  wild  boar,  Sus  cristatus. 

The  common  house  cat  has  a  complicated  ancestral  history. 
Its  remote  ancestor  was  probably  the  Egyptian  cat,  Felis  libyca, 
from  which  the  Mediterranean  cat,  F.  mediterranea,  the  wild- 
cat, F.  catus,  the  jungle  cat,  F.  chaus,  the  steppe  cat,  F.  catidata, 
and  the  Indian  desert  cat,  F.  ornata,  descended.  The  European 
and  American  domesticated  cats  were  derived  either  from  the 
Eg3^tian  cat  or  the  Mediterranean  cat,  which  soon  became 
crossed  with  the  wildcat.  The  spotted  Indian,  domesticated 
cats  are  derived  from  the  Indian  desert  cat.  A  number  of  crosses 
have  been  made  between  the  various  wild  and  domesticated  cats, 
resulting  in  a  large  variety  of  mixed  breeds. 

g.   Fossil  Mammals 

Fourteen  of  the  thirty-two  orders  of  mammals  are  known  only 
from  fossil  forms  (H.  F.  Osborn).  The  earliest  known  remains 
of  mammals  are  from  the  Triassic  period,  a  period  which  began 
about  ten  million  years  ago  (see. Table  XVII).  The  genera 
Dromatherium  and  Micronodon,  taken  in  the  Upper  Triassic  of 
North  America,  have  been  referred  tentatively  to  the  first  order 
of  mammals,  the  Protodonta.  The  mammals  of  both  the 
Triassic  and  Jurassic  periods  were  small.  A  number  of  genera 
of  marsupials  (Multituberculata)  and  the  lowest  placental 
mammals,  the  Trituberculata  or  Mesozoic  insectivores,  are 
referred  to  the  Jurassic  period.  In  Cretaceous  times  the  evolu- 
tion of  the  existing  orders  of  placental  mammals  took  place. 
There  are,  however,  very  few  remains;  the  genera  Ptilodus  and 
Meniscoessus  are  marsupials  (Multituberculata)  from  the 
Upper  Cretaceous  of  North  America.  ' 


686 


COLLEGE  ZOOLOGY 


The  Cenozoic  Era  is  called  the  "  Age  of  Mammals,"  since  this 
interval  of  about  three  million  years,  between  the  Mesozoic  Era 
and  the  present  time,  witnessed  the  ascendency  of  mammals  and 
the  inauguration  of  their  dominance  over  all  other  animals.  The 
mammalian  characteristics  of  the  periods  in  the  Cenozoic  Era 
may  be  outlined  briefly  as  follows  (Osborn):  — 

The  Eocene  is  "  characterized  by  the  first  appearance  of  many 
of  the  ancestors  of  the  modernized  mammals  and  the  gradual  dis- 
appearance of  many  of  the  archaic  types  characteristic  of  the  Age 
of  Reptiles  "  (Mesozoic  Era). 

The  Oligocene  is  "  characterized  by  the  appearance  of  many 
existing  types  of  mammals  and  the  gradual  disappearance  of 

many  of  the  older 
types." 

The  Miocene  is 
an  early  stage  of 
modernization, 
"  in  which  lived 
many  mammals 
closely  similar  to 
existing  forms.' 

The      Pliocene 

witnessed ''  avast 

modernization  of  the  mammals  in  which  all  the  existing  orders 

and  families  are  known,  as  well  as  many  of  the  existing  genera, 

but  few  or  no  existing  species." 

The  Pleistocene  is  "  a  life  period  in  which  the  majority  of  the 
recent  forms  of  mammals  appear  and  in  which  there  occurs  the 
last  glacial  period  and  a  great  natural  extinction  of  earlier  forms 
in  all  parts  of  the  world." 

The  Holocene,  or  recent  time,  is  "  characterized  by  the  world- 
wide destruction  and  elimination  of  mammals  through  the  agency 
of  man." 

Among  the  fossil  mammals  found  in  North  America  are  the 
archaic  ungulate,  Uintatherium  mirabile  (Fig.  548),  which  was 


Fig.  548.  —  Skeleton  of  Uintatherium  mirabile. 
(From  Flower  and  Lydekker,  after  Marsh.) 


CLASS  MAMMALIA  687 

about  as  large  as  the  largest  existing  elephants,  and  possessed 
three  pairs  of  conspicuous  protuberances  upon  the  dorsal  surface 
of  its  head;   the  enormous  tortoise  armadillo,  Glyptodon  davipes 


Fig.  549.  —  Glyptodon  davipes,  a  fossil  edentate  resembling  the  armadillo. 
(From  Weysse,  after  Owen.) 

(Fig.  549),  which  was  almost  nine  feet  in  length,  and  was  pro- 
vided with  an  arched  shell  of  immovable  bony  plates;  and  the 
mastodon  (Fig.  550),  of  Europe,  Asia,  and  South  Africa,  as  well 


Fig.  550.  —  Restoration  of  Mastodon  arvernensis.     (From  H.  F.  Osborn.) 

as  of  North  America,  which  resembled  our  modern  elephants  in 
size  and  shape,  and  of  which  more  than  thirty  species  have  been 
distinguished. 


688  COLLEGE  ZOOLOGY 

h.    The  Economic  Importance  of  Mammals 

The  relations  of  mammals  to  man  are  so  varied  and  complex 
that  only  a  very  general  account  can  be  given  here.  In  the  first 
place,  DOMESTIC  MAMMALS  are  of  almost  inestimable  value  to  man. 
Cattle  constitute  the  most  important  animal  industry  in  this 
country.  Next  in  importance  to  cattle  are  horses.  Sheep  are 
utilized  extensively  for  meat  and  wool.  In  some  countries  goats 
are  used  as  draft  animals  and  furnish  milk  and  meat.  In  the 
tropical  countries  of  the  Old  World,  especially  in  desert  regions, 
the  camel  is  the  most  important  draft  animal;  its  hair  is  valuable 
in  the  manufacture  of  fabrics  and  brushes.  In  parts  of  South 
America  the  llama  and  guanaco  furnish  the  chief  means  of  trans- 
portation. The  elephant  is  in  Asia  used  as  a  draft  animal,  for 
hunting,  and  for  various  other  purposes;  in  Africa  it  is  hunted 
for  the  ivory  in  its  tusks. 

The  GAME  ANIMALS  are  those  that  are  pursued  and  taken  by 
sportsmen.  Some  of  the  more  important  game  mammals  of 
North  America  are  the  moose,  wapiti,  deer,  bears,  mountain  lions, 
foxes,  wolves,  coyotes,  wildcats,  and  rabbits.  Some  of  these  are 
exceedingly  destructive,  and  certain  states  pay  a  bounty  for  their 
capture;  others,  like  the  deer,  are  of  considerable  value  as  food, 
though  they  may  be  injurious  to  farms  in  thickly  populated 
districts.  The  various  states  protect  many  of  the  game  animals 
during  certain  seasons  of  the  year  and  in  some  cases  for  a  period 
of  years,  so  as  to  prevent  their  extermination. 

The  majority  of  the  fur-bearing  animals  of  North  America 
belong  to  the  family  Mustelid.^  of  the  order  Carnivora.  This 
family  includes  the  otter,  mink,  weasel,  marten,  wolverine,  and 
badger.  Most  of  these  animals  are  now  scarce,  and  furriers  are 
forced  to  use  the  skins  of  other  species,  such  as  the  skunk, 
muskrat,  raccoon,  fox,  lynx,  black  bear,  and  rabbit.  The  skins 
of  some  mammals  command  almost  fabulous  prices;  for  example, 
the  pure  black  skins  of  the  fox  range  from  $500  to  $2000  each. 

The  RoDENTiA,  or  gnawing  mammals,  are  on  the  whole  in- 


CLASS  MAMMALIA  6Sg 

jurious,  since  they  include  such  notorious  pests  as  the  rabbits, 
rats,  and  mice.  Rabbits  are  vegetarians,  feeding  on  leaves, 
stems,  flowers,  seeds,  buds,  batk,  and  fruit.  They  damage 
especially  clover,  alfalfa,  peas,  cabbages,  and  the  bark  of  trees. 
Young  fruit,  forest,  and  ornamental  trees  and  shrubs  in  nurseries 
are  subject  to  injury  from  rabbits,  and  frequently  the  branches 
and  twigs  within  reach  are  cut  off,  or  the  bark  is  removed  near 
the  base  of  the  trunk,  thus  girdling  the  tree  and  causing  its  death. 
Mice  feed  principally  on  stems,  leaves,  seeds,  bulbs,  roots,  and 
other  kinds  of  vegetation.  A  single  field  mouse  devours  in  one 
year  from  twenty  to  thirty-six  pounds  of  green  vegetation,  and 
a  thousand  mice  in  one  meadow  would  require  at  least  twelve 
tons  annually.  Damage  is  done  to  meadows  and  pastures,  to 
grains  and  forage,  to  garden  crops,  to  small  fruits,  to  nursery 
stock,  to  orchards,  to  forest  trees,  and  to  parks  and  lawns. 

"  The  RAT  is  the  worst  mammalian  pest  known  to  man.  Its 
depredations  throughout  the  world  result  in  losses  amounting  to 
hundreds  of  millions  of  dollars  annually.  But  these  losses,  great 
as  they  are,  are  of  less  importance  than  the  fact  that  rats  carry 
from  house  to  house  and  from  seaport  to  seaport  the  germs  of 
the  dreaded  plague."  (Lantz.)  The  amount  of  loss  due  to  rats 
in  the  United  States  is  not  known;  in  Germany  the  loss  is  esti- 
mated at  $50,000,000  per  year.  The  losses  in  this  country  are 
as  follows:  a  large  part  of  the  crops  of  cultivated  grains  are  often 
destroyed  by  rats;  "  the  loss  of  poultry  due  to  rats  is  probably 
greater  than  that  inflicted  by  foxes,  minks,  weasels,  skunks, 
hawks,  and  owls  combined  "  (Lantz);  rats  are  a  serious  pest  in 
game  preserves,  feeding  upon  the  eggs  and  young  of  pheasants, 
etc. ;  fruits  and  vegetables  both  before  and  after  being  gathered 
are  damaged  by  rats;  and  miscellaneous  merchandise  in  stores, 
markets,  and  warehouses  suffers  injuries  second  only  to  that  done 
to  grains.  Rats  eat  bulbs,  flowers,  and  seeds  in  greenhouses, 
set  fire  to  buildings  by  gnawing  matches,  depreciate  the  value 
of  buildings  and  furniture,  and  are  injurious  in  many  other 
ways. 


690  COLLEGE  ZOOLOGY 

Predaceous  mammals  feed  upon  the  flesh  of  other  animals; 
if  these  animals  are  beneficial  to  man,  the  predaceous  mammal 
may  be  considered  injurious,  but  if  the  animals  preyed  upon  are 
harmful  to  man,  the  predaceous  mammal  is  beneficial.  The 
harmful  predaceous  mammals  include  the  wolves  and  cougars, 
which  subsist  largely  upon  big  game,  sheep,  cattle,  and  horses, 
and  the  house  cat,  which  destroys  millions  of  birds  in  this  country 
annually. 

The  other  predaceous  mammals  are  occasionally  harmful, 
but  usually  beneficial.  Coyotes  and  wildcats,  if  poultry  and 
sheep  are  properly  protected,  devote  their  attention  to  rabbits 
and  other  small  mammals,  and  insects.  The  fox  destroys  great 
numbers  of  field-mice,  rabbits,  ground  squirrels,  and  insects. 
The  mink  often  commits  depredations  upon  poultry,  but  more 
than  pays  for  this  by  destroying  meadow-mice  and  muskrats. 
The  weasel  has  a  similar  bill  of  fare.  The  skunk  destroys  im- 
mense numbers  of  mice,  grubs,  and  noxious  insects.  The  badger 
feeds  largely  upon  ground  squirrels  and  other  burrowing  mammals 
and  insects. 

There  is  great  danger  in  introducing  mammals  into  this 
country.  The  brown  rat  reached  this  country  about  1775,  and 
is  now,  as  pointed  out  above,  our  worst  mammalian  pest.  Rab- 
bits which  were  introduced  into  Australia  about  1864  soon  be- 
came so  numerous  that  legislative  action  was  taken  for  their 
destruction.  The  mungoose  of  India  destroys  rats,  lizards, 
and  snakes;  it  was  introduced  into  Jamaica  and  other  tropical 
islands  and  at  first  proved  very  beneficial,  but  later  it  became 
a  great  pest,  destroying  poultry,  birds,  young  domesticated 
animals,  and  even  fruit.  These  disastrous  results  from  the 
introduction  of  foreign  species  of  mammals  led  Congress  to 
prohibit  the  importation  of  most  reptiles,  birds,  and  mammals 
imless  special  permission  is  obtained  from  the  Department  of 
Agriculture. 


CHAPTER    XXII 

THE  ANCESTORS   AND   INTERRELATIONS   OF  THE 
VERTEBRATES 

The  purpose  of  this  chapter  is  to  point  out  the  probable  re- 
lations between  the  vertebrates  and  invertebrates,  to  unify  our 
account  of  the  vertebrates  by  discussing  the  interrelations  of 
the  class,  and  to  indicate  the  extent  of  our  knowledge  concerning 
the  ancestors  of  vertebrates  secured  by  the  study  of  fossil  forms. 

I.   The  Relations  between  Vertebrates  and 
Invertebrates 

A  problem  that  has  commanded  the  attention  of  many  emi- 
nent scientists  has  been  to  trace  the  ancestry  of  the  vertebrates 
to  some  invertebrate  form.  Investigations  along  this  line  have 
resulted  in  a  number  of  theories,  each  with  many  adherents 
ready  to  argue  in  its  favor.  It  is  impossible  in  this  place  to  give 
an  account  of  each  of  these  theories,  but  that  their  differences 
are  considerable  may  be  inferred  from  the  fact  that  scientists 
have  derived  the  vertebrates  from  the  annelids,  nemerteans, 
insects,  arachnids,   flatworms,  and  echinoderms. 

The  origin  of  vertebrates  from  the  echinoderms  through  the 
Enteropneusta  (p.  386,  Fig.  332)  and  Amphioxus  (p.  394,  Fig. 
341)  seems  to  have  so  many  points  in  its  favor  that  this  theory 
will  be  sketched  briefly  in  the  following  paragraphs  as  an  illustra- 
tion of  the  method  used  in  tracing  vertebrate  descent. 

We  have  seen  that  there  are  a  number  of  subphyla  in  the 
phylum  Chordata  that  contain  animals  of  a  lower  grade  than 
the  vertebrates.  These  are:  (i)  the  Enteropneusta  (Figs. 
332-336),  which  includes  a  few  worm-like  species;  (2)  the  Tuni- 

691 


692  COLLEGE  ZOOLOGY 

CATA  (Figs.  337-340),  which  contains  a  number  of  sac-like  animals 
that  exhibit  chordate  characteristics  chiefly  in  the  immature 
stages;  and  (3)  the  Cephalo chorda,  which  has  but  a  single 
genus  —  Amphioxus  (Figs.  341-344). 

A  careful  study  of  Amphioxus  has  brought  forth  convincing 
evidence  that  this  animal  is  really  a  modified  ancestor  of  the 
vertebrates.  The  essential  structural  characteristics  which  are 
possessed  in  common  by  Amphioxus  and  the  vertebrates  are 
the  presence  of  (i)  a  notochord,  (2)  a  dorsal  nervous  system, 
(3)  a  pharynx  perforated  by  gill-slits,  and  (4)  a  mid-ventral 
endostyle. 

If  we  accept  Amphioxus  as  the  invertebrate  most  nearly  allied 
to  the  vertebrates,  we  may  then  seek  for  an  ancestor  of  this  form. 
Such  an  ancestor  is  supplied  by  the  sea-squirts  or  Tunicata 
(pp.  389  to  393).  The  adult  tunicates  (Fig.  7,^8)  have  retained 
very  few  of  their  primitive  characteristics,  but  the  larva,  as 
shown  in  Figure  339,  possesses  a  typical  notochord,  a  neural  tube, 
a  series  of  gill-slits,  and  an  endostyle,  which  are  similar  in  posi- 
tion and  development  to  these  structures  in  Amphioxus ;  and  it 
seems  probable  that  the  adult  tunicate  once  existed  as  an  ani- 
mal like  the  larval  tunicate  of  to-day,  and  that  this  remote  an- 
cestor was  not  only  the  progenitor  of  the  modern  tunicates,  but 
was  also  the  direct  ancestor  of  the  group  to  w^hich  Amphioxus 
belongs. 

The  search  for  a  vertebrate  ancestor  more  remote  than  the 
tunicates  leads  to  a  consideration  of  the  marine  worm-like  ani- 
mals of  the  subphylum  Enteropneusta.  These  species,  as 
previously  shown  (pp.  386  and  389,  Figs.  332  and  :^s3)j  2-re  pro- 
vided with  clearly  defined  gill-slits,  a  structure  which  may  be 
homologous  to  the  notochord  of  the  vertebrates,  and  four 
longitudinal  nerve-cords  of  which  the  dorsal  is  slightly  more 
pronounced  than  the  ventral  and  lateral  ones.  It  appears, 
therefore,  that  the  Enteropneusta  may  possibly  be  vertebrate 
ancestors  of  an  earlier  stage  than  the  tunicates. 

We  must  look  to  the  larvae  of  the  Enteropneusta  for  the 


ANCESTORS  AND   INTERRELATIONS  OF  VERTEBRATES     693 

link  which  may  connect  this  lowest  of  the  chordates  with  the 
invertebrates  and  thus  complete  our  hypothetical  line  of 
vertebrate  descent.  The  egg  of, the  enteropneuston  Balano- 
glossus  develops  into  a  small  larv^a  called  Tornaria  (Fig.  334), 
which  floats  in  the  sea,  is  transparent,  has  a  bilateral  sym- 
metry, and  is  provided  with  bands  of  cilia  for  locomotion. 
This  larv^a  corresponds  in  habitat  and  structure  almost  exactly 
to  the  larvae  of  the  starfish  and  other  echinoderms.  This 
similarity  leads  to  the  conclusion  that  a  form  resembling  these 
larvae  was  the  very  remote  progenitor  of  both  the  echinoderms 
and  the  chordates,  and  that  "  The  lineal  descendants  of  this 
hj'pothetical  ancestor  chose  two  paths,  the  one  leading  to  the 
EcinNODERMATA,  the  other  to  Balanoglossus,  the  Tunicata, 
Amphioxus,  and  eventually  the  Vertebrata." 

"  The  question  of  the  descent  of  the  Chordata  is  not  solved 
by  acceptin-g  their  relationship  to  the  Enteropneusta,  since 
this  latter  group  holds  an  uncommonly  isolated  position.  Only 
from  the  structure  of  the  Balanoglossus  larva  can  there  be  con- 
cluded a  distant  connection  with  the  echinoderms.  We  must 
resign  ourselves  to  the  thought  that  at  the  present  time  we  are 
not  in  a  condition  to  assert  from  what  ancestral  form  the  Chor- 
data, and  with  them  Balanoglossus,  are  to  be  derived.  The 
origin  of  the  vertebrates  is  lost  in  the  obscurity  of  forms  un- 
known to  us."     (Wilder.) 

2.  The  Phylogenesis  of  Vertebrates^ 

Anatomical  and  paleontological  investigations  are  continually 
changing  our  ideas  regarding  the  interrelations  of  the  verte- 
brates, and  wT  can  indicate  only  provisionally  the  possible  line 
of  descent  of  the  vertebrates  and  the  relations  of  one  group  to 
another.  Reference  to  Figure  551  will  make  the  following 
paragraphs  clear. 

The  lowest  vertebrates,  i.e.  the  forms  most  nearly  related  to 

1  For  a  more  detailed  account  of  this  subject,  see  Wilder's  History  of  the  Hu- 
man Body,  Chapter  II. 


694 


COLLEGE  ZOOLOGY 


^'^placentaliaN,^ 


I         MARSU 


Fig.  551. — Phylogenetic  tree  of  vertebrates.  Double  underscoring  in- 
dicates an  extinct  group;  single  underscoring,  those  that  have  but  a  few 
living  representatives.  The  boundaries  of  the  classes  are  represented  by 
dotted  lines.     (Modified  after  Wilder.) 


ANCESTORS  AND   INTERRELATIONS  OF  VERTEBRATES     695 

Amphioxus,  are  the  Cyclostomes.  These  (see  Chap.  XV, 
Fig.  352)  are  eel-like  vertebrates  without  jaws  and  with  a  carti- 
laginous skeleton.  Next  above  Jthe  Cyclostomes  come  the 
Elasmobranchs  (sharks,  skates,  etc. ;  see  Chap.  XVI,  Fig. 
358),  which  also  possess  a  cartilaginous  skeleton,  but  are  provided 
with  jaws.  The  direct  descendants  of  the  ELASiJioBRANCHS 
appear  to  be  the  ganoid  fishes  (Chondrostei,  Crossopterygii, 
Lepidostei,  and  Amioidei),  which  constituted  the  dominant 
group  during  the  Devonian  Period  (see  Table  XVII).  Some 
of  the  ganoids  have  a  skeleton  entirely  of  cartilage;  others  are 
equipped  with  both  cartilage  and  bone,  but  all  of  them  possess 
gill-covers,  which  are  absent  in  Cyclostomes  and  Elasmo- 
branchs. The  bony  fishes  (Teleosts)  are  probably  the  de- 
scendants of  the  bony  ganoids.  The  lung-fishes  (Dipnoi)  rep- 
resent an  independent  lateral  branch  from  the  Elasmobranchs; 
they  are  by  many  considered  a  connecting  link  between  the  fishes 
and  amphibians,  but  this  is  probably  not  the  case. 

The  Amphibians  may  be  traced  back  to  the  ganoids  and  seem 
to  have  developed  into  the  Stegocephalia,  a  group  now  extinct, 
which  are  the  probable  ancestors  of  not  only  the  modern  Am- 
phibia, but  also  of  the  Reptilia. 

The  most  primitive  living  reptiles  are  the  Rhynchocephalia; 
these  are  represented  by  the  single  living  species  Sphenodon 
punctatum  (Fig.  450)  of  New  Zealand.  From  this  group  have 
come  the  Squamata,  Serpe'ntes,  and  Crocodilini,  and  some 
of  the  extinct  reptiles.  The  Testudinata  seem  more  closely 
allied  to  the  extinct  Theromorpha. 

The  birds  have  sprung  from  dinosaurian  ancestors.  They  are 
very  closely  related  to  the  reptiles,  and  the  earliest  known  form 
(ARCHiEOPTERYx)  might  almost  be  called  a  flying  reptile.  The 
toothed  birds  are  considered  the  forerunners  of  the  modern 
toothless  birds. 

The  Mammalia  are  of  special  interest,  since  this  class  of  ver- 
tebrates includes  man.  The  earliest  living  mammals,  the 
Monotremata,   are   descended   from   reptilian    ancestors,   the 


696  COLLEGE  ZOOLOGY 

Theromorpha,  which  are  known  only  from  fossil  remains. 
Above  the  monotremes  are  placed  the  Marsupialia,  and  finally 
the  Placentalia,  which  are  the  highest  of  all  animals.  The 
Primates,  the  group  that  includes  man,  seem  to  have  descended 
from  the  primitive  Insectivora.  The  line  of  descent  within 
the  group  is  probably  somewhat  as  follows:  — 

1.  MoNOTREMATA.     Egg-laying  Mammals. 

2.  Marsupialia.     Marsupials. 

3.  Insectivora.     Insectivores. 

4.  LEMURiDiE.     Lemurs. 

5.  CERCOPiTHECiDyE.     Old  World  Monkeys  with  Tails. 
'  6.   SiMiiD^.     Anthropoid  Apes. 

7.  Pithecanthropus.     An  Extinct  "  Ape-Man." 

8.  Homo    neanderthalensis.      The    Extinct    Neanderthal 

Man. 

9.  Homo  sapiens.     Modern  Man. 

3.  The  Fossil  Remains  of  Vertebrates 

a.  Succession  of  Life  in  General 

The  fossil  remains  of  animals  that  lived  millions  of  years  ago 
give  us  authentic  records  of  the  fauna  present  upon  the  earth's 
surface  at  that  time.  These  records,  unfortunately,  are  frag- 
mentary, since  only  the  hard  parts  of  the  animals  were  preserved, 
and  these,  when  discovered,  are  almost  always  broken  and  in- 
complete, making  the  reconstruction  of  many  parts  necessary. 
From  the  evidence  obtained  from  fossils,  paleozoologists  have 
constructed  a  table  (Table  XVII)  showing  the  geological  periods, 
arranged  in  the  order  of  their  succession,  and  the  time  of  origin 
of  the  different  groups  of  animals. 

Such  a  table  shows  that  the  invertebrates  appeared  first,  since 
their  remains  occur  in  the  oldest  strata,  unaccompanied  by  the 
remains  of  vertebrates;  that  the  invertebrates  became  more 
complex  in  the  succeeding  periods;  that  the  fishes  (low  in  the 
scale  of  vertebrate  life)  were  the  first  vertebrates  to  appear; 


ANCESTORS  AND   INTERRELATIONS   OF   VERTEBRATES     697 

and  that  these  were  followed  by  the  amphibians,  reptiles,  birds, 
and  mammals  in  just  the  order  that  would  be  expected  from  a 
study  of  the  structure  of  these  vertebrates. 

TABLE  XVII 

the  distribution  of  the  fossil  remains  of  animals  in  the 
earth's  crust 


Era 


Cenozoic 
(Era  of 
Mammals) 


Mesozoic 
(Era  of 
Reptiles) 


Paleozoic 
(Era  of 
Invertebrates) 


Archaean 


Period 


Recent 

Pleistocene 

Pliocene 

Miocene 

Eocene 


Cretaceous 

Jurassic 
Triassic 


Permian 

Carboniferous 
(Age   of   Am- 
phibians) 

Devonian  (Age 
of  Fishes) 

Silurian  (Age  of 
Invertebrates) 


Cambrian 


Laurentian 


Animals  Characteristic  of  the  Period 


Man;   mammals,  mostly  of  species 

still  living. 
Mammals   abundant;    belonging   to 
numerous  extinct  families  and  orders. 


Bird-like  reptiles;  flying  reptiles; 
toothed  birds ;  first  snakes ;  bony- 
fishes  abound;  sharks  again  nu- 
merous. 

First  birds ;  giant  reptiles ;  clams  and 
snails  abundant. 

First  mammals  (a  marsupial) ;  sharks 
reduced  to  few  forms;  bony-fishes 
appear. 


Life  transitional  between  Paleozoic 
and  Mesozoic  eras. 

Earliest  true  reptiles.  Amphibians; 
lung-fishes ;  first  crayfishes ;  insects 
abundant ;  spiders ;  freah-water 
mussels. 

First  amphibian;  sharks;  first  land 
shells  (snails) ;  mollusks  abundant ; 
first  crabs. 

First  truly  terrestrial  or  air-breathing 
animals ;  first  insects ;  corals  abun- 
dant; mailed  fishes;  brachiopods; 
trilobites ;  mollusks. 

Invertebrates  only. 


Simple  marine  invertebrates. 


698  COLLEGE   ZOOLOGY 

h.    The  Evolution  of  the  Horse  ^ 

One  of  the  best  methods  of  illustrating  the  value  of  studying 
fossil  animals  is  to  give  a  brief  description  of  a  succession  of  con- 
necting links  such  as  are  exhibited  by  the  evolution  of  the  horse. 
The  horses  now  inhabiting  America  are  descendants  of  domesti- 
cated animals  which  were  brought  to  this  country  by  the  early 
settlers  from  Europe,  but  in  prehistoric  times  the  ancestors  of 
our  modern  horse  were  native  here,"  and  some  of  the  finest  fossil 
remains  of  these  ancestors  have  been  found  in  America. 

The  evolution  of  the  horse  has  been  traced  back  through  at 
least  twelve  distinct  stages  extending  through  the  Cenozoic  Era 
or  the  Era  of  Mammals.  A  brief  description  of  five  of  these 
stages  together  with  Figure  552  will  serve  to  illustrate  the  prin- 
cipal changes  that  took  place  during  this  evolution.  The 
structural  features  that  became  modified  during  this  era  of  about 
3,000,000  years  were  such  as  to  adapt  the  horse  to  life  on  the 
open  plains,  where  its  food  consisted  of  dry  silicious  grasses. 

The  feet  gradually  lost  the  side  toes,  and  only  the  middle  toe 
and  splints  of  the  second  and  fourth  digits  remain  in  our  modern 
horses.  The  limbs  became  longer,  enabling  the  animal  to  move 
about  more  rapidly;  this  change  was  correlated  with  an  elonga- 
tion of  the  head  and  neck,  which  was  necessary  in  order  to  reach 
the  ground.  The  front  teeth  were  modified  as  chisel-like  crop- 
ping structures,  and  the  back  teeth  evolved  from  simple  molars 
into  wonderfully  effective  grinding  organs  with  tortuous  ridges 
of  enamel  and  with  supporting  and  protecting  layers  of  dentine 
and  cement.  During  the  later  periods  the  molars  elongated, 
and  thus  became  adapted  for  grinding  the  dry  silicious  grasses 
which  caused  them  to  wear  down  more  rapidly  than  the  softer 
vegetation.  During  this  evolution  the  body  gradually  increased 
in  size  from  that  of  the  earliest  known  form,  which  was  about  as 
large  as  a  domestic  cat,  to  that  of  the  horse  of  to-day. 

*  For  a  detailed  account  of  this  subject,  see  "The  Evolution  of  the  Horse"  by 
W.  D.  Matthew,  Sup.  to  Am.  Museum  Journ.,  Vol.  3,  1903.     Guide  Leaflet,  No.  9, 


ANCESTORS  AND   INTERRELATIONS   OF  VERTEBRATES     699 


700 


COLLEGE  ZOOLOGY 


(i)  Hyracotherium  and  Eohippus  (Fig.  553).  These  animals 
lived  during  the  lower  Eocene  Period.  Only  the  skull  of  Hyraco- 
therium  has  been  discovered,  but  this  shows  it  to  be  the  most 
primitive  stage  known.  Eohippus  was  named  from  remains 
found  in  the  Lower  Eocene  of  Wyoming  and  New  Mexico;  its 
forefeet  have  four  complete  toes  and  the  splint  of  the  fifth,  and 


Fig.  553-  —  Restoration  of  the  four-toed  horse,  the  oldest  known  ancestor  of 
the  modern  horse;   only  16  inches  high.     (From  Matthew^  after  Knight.) 


the  hind  feet  have  three  complete  toes  and  the  splint  of  the 
fifth. 

(2)  Protorohippus  and  Orohippus.  These  forms  lived  during 
the  Middle  Eocene  Period  and  were  about  as  large  as  a  small  dog. 
The  feet  are  similar  to  those  of  Eohippus,  except  that  the  splint  of 
the  fifth  digit  has  entirely  disappeared.  Remains  of  an  animal 
called  Epihippus  are  recorded  from  the  Upper  Eocene. 

(3)  Mesohippus.  This  animal  belongs  to  the  Oligocene  Period, 
and  reached  the  size  of  a  sheep.     Its  fore  feet  possess  three 


ANCESTORS  AND   INTERRELATIONS   OF  VERTEBRATES     701 

complete  toes  and  a  splint  of  the  fifth  digit,  and  the  hind  feet 
also  possess  three  complete  toes,  but  no  splint.  All  three  toes 
touched  the  ground,  but  the  middle  toe  is  larger  and  bore  most 
of  the  weight  of  the  body.  Anchitherium  from  the  Lower  Mio- 
cene is  larger  than  Mesohippus ;  Parahippus  and  Hypohippus 
from  the  Middle  Miocene  were  as  large  as  a  Shetland  pony. 

(4)  Protohippus  and  Pliohippus.  In  these  animals  from  the 
Middle  and  Upper  Miocene  there  are  three  toes  on  each  foot,  but 
the  middle  one  is  large,  and  the  side  toes  are  smaller  and  do  not 
touch  the  ground.  The  crowns  of  the  upper  molars  are  long  and 
provided  with  an  effective  grinding  surface  of  ridges  of  cement. 
Hipparion  which  lived  during  the  Pliocene  Period  is  larger  than 
Protohippus  and  has  a  more  complicated  tooth  pattern. 

(5)  Eqims.  The  modern  horses  of  the  Pleistocene  and  Recent 
periods  have  lost  the  first  and  fifth  digits  entirely,  and  the  second 
and  fourth  digits  are  represented  by  splints.  The  third  toe 
alone  sustains  the  weight  of  the  body.  The  crowns  of  the  molar 
teeth  are  much  elongated,  the  skull  has  lengthened,  and  the  body 
is  considerably  larger  than  that  of  any  of  its  ancestors. 

At  the  present  time  true  wild  horses  occur  only  in  Asia  (the 
Asiatic  Wild  Ass,  Equus  hemionus,  and  Przewalsky's  Horse,  E. 
pryzeivalskii)  and  in  Africa  (the  African  Wild  Ass,  E.  asinus,  and 
the  Zebras,  E.  zebra,  E.  burchelli,  and  E.  quagga).  The  mus- 
tangs and  broncos  of  our  Western  Plains  and  South  America  are 
not  true  wild  horse,  but  are  descendants  of  domesticated  horses 
brought  over  from  Europe. 

The  evolution  of  the  elephant,  dog,  and  many  other  animals 
has  been  carefully  w^orked  out  by  paleontologists,  but  none  quite 
so  much  in  detail  as  that  of  the  horse.  Nevertheless,  they  show 
how  much  is  possible  toward  a  knowledge  of  the  ancestors  of 
vertebrates  from  a  study  of  fossil  forms. 


INDEX 


All  numbers  refer  fo  pages.  Words  in  italics  are  names  of  families,  genera, 
species,  or  of  higher  divisions.  Numbers  in  thick  type  are  numbers  of  pages  on 
which  there  are  figures. 


Aard  varks,  644. 

Absorption,  482. 

AcanthiidcB,  348. 

Acanthocephala,  180. 

Acanthodaclylus,  538. 

Acanthopterygii,  444. 

Acarina,  379-381. 

Accipiter,  605,  606. 

Accretion,  10. 

Acetabulum,  404,  496. 

Achorutes,  338. 

Achtheres,  294. 

Acicula,  235. 

Acinonyx,  656. 

Acipenser,  453;  Acipenserida,  443,  453. 

Acmoea,  258. 

Accelomata,  241. 

Acontia,  136. 

Acraspedote,  129. 

Acridiidte,  345;  Acridium,  legs,  332. 

Acris,  512,  519,  520. 

Actiniaria,  135,  141. 

Actinomma,  40. 

Actinophrys,  40. 

ActinosphcBrium,  40. 

Actinozoa,  133. 

Aditis,  607,  608. 

Adductor  muscles,  244,  245. 

Adelochorda,.2,?>(i. 

Adephaga,  360. 

Admetus,  381. 

Adrenals,  492. 

jEpyornis,  589;    Mpyornithiformes,  589, 

598. 
AgamidcB,  537,  553. 
AgelenidcB,  377. 
Agkistrodon,  539;  ^.  contortrix,  566;   .4. 

piscivorus,  565,  566. 


703 


Aglossa,  512,  518;  Aglossidce,  512,  518. 

Aglypha,  539,  560. 

Air-bladder,  433,  439;   -sac,  585. 

.4iX  603. 

AlaudidcB,  591. 

Albatross,  590,  600. 

Alcedinidce,  591,  611;  .4/ce5,  644; 
AlcidcR,  590,  607,  609. 

/1/cej,  669. 

Alcyonacea,  139,  140. 

Alcyonaria,  139. 

Alcyonium,  139,  140. 

J/c/io,  354. 

Alimentary  canal,  405  (see  digestive 
system). 

AUantois,  680,  681. 

Alligator,  536,  547,  548,  549s 

Allogromia,  41. 

Allolobophora,  215,  236. 

Alouatta,  664. 

Alpheus,  297. 

Alternation    of    generations,     81 
132. 

Alytes,  512,  522. 

Ambloplitcs,  467. 

AmblyoposidcB,  444,  462 ;  Amblyopsis,  462, 
463. 

Amblyrhynchus,  554. 

Ambulacral  grooves,  191. 

.4  mby stoma,  511,516;  ^  mbystomidcB,  511, 
S16. 

Ameba  proteus,  27-39 ;  anatomy,  28 ; 
behavior,  33 ;  locomotion,  35 ;  metab- 
olism, 29;   reproduction,  32. 

Ameiurus,  457. 

Ameiva,  538. 

Ametabola,  334. 

^wia,  454,  455;  Amiidce,  443,  454. 


122. 


704 


INDEX 


Amicula,  252. 

Amitosis,  14. 

Ammocoetes,  419, 

Ammophila,  368. 

A mmos pernio philus,  658. 

Ammothea,  384. 

Amnion,  680,  68i. 

Atnniota,  680. 

Amoebocytes,  196. 

Amphiaster,  15. 

Amphibia,  400,  477-526,  694,  695 ;  breed- 
ing habits,  524;  classification,  510; 
colors,  522 ;  economic  importance,  526 ; 
hibernation,  524;  poisonous,  525 ;  pre- 
historic, 52s;  regeneration,  523;  re- 
view of  orders  and  families,  512-522. 

Amphiblastula,  97,  98. 

Amphineura,  243,  251-252. 

Amphioxus,  393,  394,  691,  692,  693  (see 
Cephalochorda). 

AmphipnoidcB,  444. 

Amphipoda,  296,  297,  298. 

Amphisbcena,  538;  AmphisbcEnidce,  538, 
557- 

Amphitrite,  235,  236. 

Amphiuma,   511,    514;    Amphiumoidece, 

Amphiura,  189. 

Ampulla,  192,  193. 

Amylopsin,  482. 

Anabolisra,  19,  29. 

Anaconda,  559. 

Analogous  organs,  76. 

Anamniota,  680. 

Anaphase  of  mitosis,  15,  16. 

Anaphothrips,  342. 

Anas  boscas,  630. 

Anaspidacea,  294;  Anaspides,  294. 

Anatidce,  590,  603;  Anatince,  603. 

Anatomy,  26. 

Ancestors,  of  vertebrates,  691-701. 

Anchitherium,  701. 

Ancylostoma,  173. 

Andrena,  366;  nest,  367. 

Angler,  444,  468. 

Anguid(E,  537,  555;  Anguis,  556. 

Anguilla,    463;     Anguillidce,    444,    463; 

Anguilllformes,  444. 
Angulo-splenial,  494. 
Anhinga,  601 ;  Anhingidce,  590. 
Anisolabis,  342. 
Annelida,   215-241;    classification,   231; 


coelom,  240;  metamerism,  240;  tro- 
chophore,  241. 

Anodonla,  243-251;  anatomy,  245;  cir- 
culation, 246 ;  digestion,  246 ;  eco- 
nomic importance,  251 ;  excretory 
organs,  248  ;  external  features,  244 ; 
food,  246;  nervous  system,  249;  re- 
production, 250;    sense  organs,  249. 

Anolis,  537,  559- 

Anomolepsis,  538. 

Anopheles,  356;    and  malaria,  50;   wing, 

333 
Anosia,  351,  352. 
Anser,    630;     Anseriformes,    590,    602; 

AnserincB,  603. 
Ant,  364 ;  honey-,  369 ;  leaf  cutting,  369 ; 

white,  340. 
Ant-eater,    661 ;     Cape,    644 ;     banded, 

649;    great,  643;    scaly,  643;    spiny, 

642,  646. 
Antedon,  190. 
Antelopes,  667 

Antenna,  of  Cambarus,  278,  279 ;  honey- 
bee, 312,  313;   insects,  330;    milliped, 

309,  310;   Peripatus,  306. 
Antenna-cleaner,  314,  315 ;    comb,  314, 

315. 

Antennata,  275. 

Antennulc,  278,  279. 

Anthomedusce,  128. 

Anthozoa,  108,  133-142. 

Anthropoidea,  644,  662,  664. 

Anthropopithecus,  665,  666. 

Antilocapra,  669. 

Antimere,  90 

Antipathidea,  142. 

Ant-lion,  349. 

Anura,  511. 

Anus,  53,  55,  190,  206,  317. 

Aorta,  246,  247,  438,  485,  486. 

Ape,  696. 

Aphid,  345;  Aphidiidce,  346;  Aphis-lion, 

349 

Aphrodite,  236. 

Apidoe,   364,   366;    Apis,   312-328   (see 

honeybee). 
Aplacophora,  252. 
Apoda,  477,  510,  512,  694. 
Apodes,  444 
Apopyles,  95,  100. 
Appendages,  91 ;  of  Cambarus,  276,  277- 

281. 


INDEX 


705 


Appendicular  skeleton,  495. 

Appendicularia,  T,()i, 

Appendix,  vermiform,  638. 

Apseudes,  296,  297. 

Aptera,  337-338. 

Apteria,  578. 

Apterygijormes,  589,  598;  Apteryx,  589, 
598. 

Arachnida,  275,  276,  371-385. 

Araneida,  371-377. 

Arbacia,  190. 

Area,  262. 

Arcella,  39. 

Arch,  gill,  437  ;  hyoid,  437  ;    visceral,  437. 

Archaean  era,  697. 

ArchcBoplcryx,  592,  593,  617,  694,  695. 

Archaornithcs,  575,  588,  593. 

Archenteron,  88,  89. 

Archiannelida,  215,  232-233. 

Archigetes,  165,  166. 

Archipterygium,  446. 

Arctiidce,  353. 

Ardea,  602;  Ardeidce,  590,  602. 

Argonauta,  268,  269. 

Argulus,  294. 

Aristotle's  lantern,  203,  204. 

Armadilliutn,  297,  301. 

Armadillo,  643,  660,  661. 

Aromochelys,  535,  541. 

Artemia,  292,  293,  300. 

Arteries,  485, 486  (see  circulatory  system). 

Arthrobranchia;,  284. 

Arthropoda,  3,  24,  274-385;  classifica- 
tion, 275. 

Artiodadyla,  644,  667-671. 

AscaridcB,  173;   Ascaris,  169,  170-173. 

Ascidiacea,  390,  391-393- 

Ascon,  99,  100. 

Asellus,  296,  297. 

Aspidiotus,  346,  347. 

Aspidobranchia,  258. 

Ass,  644,  671,  684,  701. 

Assimilation,  31. 

Astacus,  276,  284. 

Asierias,  189,  190  (see  starfish). 

Asteroidea,  189,  198,  213. 

Astragalus,  497. 

Astrangia,  137. 

Astropecten,  189. 

Astrophyton,  189,  201. 

^5^Mr,  606. 

Asymmetry,  252. 


A  teles,  644,  664. 

Atheca,  535. 

Atoll,  138,  139. 

Atraclaspis,  539. 

Atriopore,     of    Amphioxus,     394,     395; 

Tunicala,  391. 
Atrium,  391,  397. 

.f4/to,  369;   AUidce,  377;  ^Wm5,  376. 
Attraction-sphere,  12,  13. 
Auditory  capsule,  416,  419 ;  ossicle,  635, 

640. 
Auk,  590,  607,  609. 
Aurelia,  129,  130. 

Auricle,  406  (see  circulatory  system). 
Auricularia,  211. 
Aurochs,  684. 
Aurophore,  126. 
Autodax,  517. 
Autolytus,  235,  236. 
Autotomy,  198,  201,  290. 
Aves,  401,  575-631,  694  (see  bird). 
Avicularia,  184. 
Avocet,  607. 
Axolotl,  516,  523. 
Aye-Ayes,  662. 

Baboon,  644. 

Badger,  655. 

Balcenida,  675. 

Balanoglossida,  386,  387;   Balanoglossus, 

214,  399,  693. 
Balantidium,  71. 
Balanus,  294,  295,  300. 
Baloena,  645,  675,  676 ;  Balcenoptera,  645, 

675,  676. 
Bandicoot,  642,  649. 
Barnacle,  300. 
Basal  disk,  109,  no,  134. 
Basepterygium,  436,  437. 
Basilarchia,  352. 
Basilingual  plate,  494. 
Basipodite,  280. 

Bass,  444,  465,  466,  467,  475,  476. 
Bats,  642,  643,  650,  651. 
Bdellostoma,  414,  420. 
Bdelloura,  156. 

Beak,  of  pigeon,  576;  of  turtle,  529,  530. 
Bears,  652,  654-655. 
Beaver,  643,  658,  659. 
Bees,  364,  366,  367. 
Beetles,  337,  347,  360-364. 
Behavior,  of  Ameba,  33;    crayfish,  290; 


2Z 


7o6 


INDEX 


echinoderms,  197,  200,  207 ;  Euglena, 
43;  frog,  506;  Hydra,  113;  Lum- 
bricus,  228 ;  Paramecium,  55  ;  Protozoa, 
68;  sponges,  102. 

Beloslomalidm,  348. 

Belugas,  674. 

Bicidium,  141. 

Bighorn,  670. 

Bile,  481;  duct,  481. 

Bills,  of  birds,  618-620. 

Binary  fission,  of  Ameba,  32,  33;  of 
Euglena,  42,  44;  Paramecium,  59. 

Biogenesis,  law  of,  302. 

Bipalium,  156. 

Bipinnaria,  197,  210,  211, 

Birds,  575-631 ;  altricial,  626;  bills,  618; 
classification,  588;  colors,  621;  do- 
mesticated, 630;  economic  imp>or- 
tance,  626;  eggs,  624;  feet,  618;  flight, 
621;  migration,  621 ;  nests,  624;  pre- 
cocious, 626;  songs,  621;  tails,  617; 
wings,  616. 

Bird,  lyre,  617 ;  man-o'-war,  601 ; 
mocking-,  591,  615;  of  paradise,  617; 
secretary,  590,  603;   tropic,  601. 

Bison,  644,  669,  670,  683. 

Bittern,  601,  602. 

Bivalve,  261. 

Blackbird,  593. 

Bladder,  urinary,  407,  440. 

Blarina,  650. 

Blastococl,  507,  508. 

Blastoderm,  87,88,  441. 

Blastoidea,  209,  210,  213. 

Blastophaga,  365. 

Blastostyle,  120,  121. 

Blastula,  87,  88,  110,  116,  507,  508. 

Blattida,  343.  ~^ 

Blissus,  348. 

Blood,  484. 

Blood-vessels,  282  (see  circulatory  sys- 
tem). 

Blubber,  675. 

Bluebird,  591 ;  -gill,  467 ;  -jay,  615 ; 
-racer,  561. 

Boa,  538,  539,  559 ;  B.  constrictor,  560 ; 
Boidce,  538,  559;   Boina,  53^. 

Boar,  671,  685. 

Bobolink,  615. 

Bob-white,  606. 

Bombinator,  512. 

Bombus,  367. 


Bombycidce,  353. 

Bombycilla,  615;    BombyciUidce,  591. 

Bombyliidce,  358. 

Bombyx,  353,  354. 

Bonasa,  606. 

Bone,  403;   cartilage,  634;  cuboid,  637; 

membrane,      634;       sesamoid,      634; 

unciform,  637. 
Boophilus,  380. 
Borer,    apple   tree,    363;     locust,    363; 

maple,  363;   wood,  361. 
Bos,  644,  684. 
Bothriocephalus,  166. 
Botryllus,  393. 
Botryoidal  tissue,  238. 
Bouton,  313. 
Bovidce,  667,  669-670. 
Bowfin,  443,  454.  455- 
Bowman's  capsule,  491. 
Brachiopoda,  185,  186. 
Brachycera,  356,  358. 
Brady  podidce,  661 ;  Brady  pus,  643. 
Brain,  408,  502  (see  nervous  system). 
Branchia,  248. 
Branchial     arch,     425;      basket,     416; 

chamber,  284;   cleft,  388;   heart,  266. 
Branchiata,  275. 
Branchiopoda,  292,  293,  299. 
Branchiosaurus,  525. 
Branchiostegite,  277,  284. 
Branchiostoma,  393,  394. 
Branchipus,  292,  293,  300. 
Braula,  328. 
Br  is  sops  is,  205. 
Bronchus,  639. 
Bronco,  701. 
Brontosaurus,  572,  573. 
Brookesia,  537,  550. 
Brow-spot,  478. 
Bruchida,  362. 
Bryozoa,  183-185. 
Bubalus,  671. 
Bubo,  6i2. 
Buccal    cavity,    218,     219,    405,    480; 

funnel,  415. 
Budding,    80;   Grantia,  94,   96;   Hydra, 

109,     no,     115;     Leucosolenia,     93; 

Metridium,  136. 
Buffaloes,  671. 

Bujo,  512,  519;  Bufonidce,  512,  519. 
Bugs,  296,  301,  343,  345,  348,  362. 
Bugula,  183,  184. 


INDEX 


707 


Bulla,  258. 

Bullhead,  457. 

Bunodes,  141. 

BuprestidcB,  361. 

Bursa  Fabricii,  576,  583. 

Burs  aria,  63. 

Buleo,  605 ;  Buteonidce,  590,  603. 

Buthus,  378,  379. 

Butterflies,  350,  351-352- 

Caeca,  374,  638;  hepatic,  195;  pyloric, 
195,  438;   rectal,  195. 

Casnolestes,  642. 

Caiman,  527,  536,  547,  548,  549. 

Calcanium,  497. 

Calcarea,  92,  105. 

Callinectes,  297,  298,  302. 

Callospermophilus,  658. 

Callotaria,  643. 

Calotes,  537,  553- 

Cambarus,  276-292 ;  appendages,  277, 
278;  autotomy,  290;  behavior,  290; 
circulatory  system,  282 ;  digestive 
system,  282 ;  distinguishing  features, 
292 ;  excretory  organs,  284 ;  external 
features,  277  ;  muscular  system,  287 ; 
nervous  system,  285 ;  regeneration, 
289 ;  reproduction,  287 ;  sense  organs, 
285. 

Camel,  644,  667 ;  Camelidcs,  667 ;  Came- 
lus,  644,  671. 

Campamdaria,  128. 

Campodea,  337,  338. 

Canals,  Bidder's,  491 ;  circumferential, 
123,  131;  epineural,  199;  inguinal, 
640;  meridional,  146,  147;  mucous, 
427 ;  nasopalatine,  637  ;  paragastric, 
146,  147 ;  perihaemal,  194 ;  radial,  95, 
100,  120,  121,  130,  131,  192,  193;  ring, 
193;  semicircular,  411 ;  of  sponges,  99, 
100;  stone,  193,  206,  207;  tentacular, 
146,  147. 

Cancer,  297. 

Candona,  294. 

CanidcB,  652,  653-654;  Canis,  22,  643, 
653,  684. 

Canines,  679. 

Canthocamptus,  294. 

Capillaries,  221,  283,  407,  438,  489. 

Caprella,  297,  298,  301. 

CaprimulgidcB,  591,  612. 

Capuchin,  644. 


Carabidce,  360 ;  Carabus,  332,  335. 

Caracara,  604,  605. 

Carapace,  of  Cambarus,  277 ;  turtle,  528, 
529. 

Carbohydrates,  11. 

Carboniferous  period,  697. 

Carcharias,  431. 

Carcharodon,  429. 

Carchesium,  65. 

Cardiac  stomach,  278,  282. 

CarettochelydidcB,  536. 

Caribou,  669. 

Carina,  580,  581, 

Carnivorq,  643,  652. 

Carp,  443,  456,  457. 

Carpals,  497. 

Carpocapsa,  355. 

Carpoidea,  209,  210,  213. 

Carpo-metacarpus,  576,  581. 

Cartilage,  74,  75 ;   Meckel's,  494. 

Cassiopea,  133. 

Cassowary,  589,  596. 

Castor,  643 ;  Castorida,  659. 

CasuariidcB,  596 ;  Casuariiformes,  589, 
596;  Casuarius,  589. 

Cat,  643,  652,  656,  685. 

Catamount,  656. 

Caterpillar,  354. 

Catfish,  443,  456,  457,  458,  475. 

Catharista,  604. 

Cathartes,  604;  CathartidcE,  590,  603. 

Catosteomi,  444. 

CatostomincE,  443,  456 ;  Catostomus,  456. 

Cattle,  644,  667,  684. 

Caudata,  477,  510,  513-517,  694. 

Caudina,  190. 

Cavia,  643. 

CebidcB,  662,  663 ;  Cebus,  644. 

Cecidomyia.  357 ;  Cecidomyiidce,  356. 

Cecropia,  353. 

Cell,  9,  12,  13-18:  definition,  17;  divi- 
sion, 14, 15,  16 ;  form,  12  ;  importance, 
18;  number,  12;  origin,  17;  physi- 
ology, 13;  size,  12;  structure,  12; 
theory,  17. 

Cement,  635,  678,  679. 

Cenozoic  Era,  686,  697. 

CentetidcB,  650. 

Centipedes^  275,  310-311. 

Centralia,  404. 

CentrarchidcB,  444,  467.  ^  ' 

Centro^ome,  12,  13,  14. 


7o8 


INDEX 


Centrum,  402,  404,  495. 

Cephalochorda,  386,  393-400;  circulatory 
system,  398;  coelom,  399;  digestive 
system,  396,  397;  excretory  system, 
399 ;  external  features,  394,  395 ;  re- 
production, 399  ;  respiration,  397, 398. 

Cephalodiscida,  386,  387  ;   Cephalodiscus, 

387,  389. 
Cephalopoda,  242,  243,  264-269. 
Cephalothorax,  277,  278,  371,  378. 
CerambycidcE,  362. 
s,        Ceratina,  366. 
\     Ceratium,  47. 

CeralodontidcB,  445,  471. 

Ceratosaurus,  572,  573. 

Cercaria,  159,  160. 

CercopilhecidcB,  662,  664,  696. 

Cere,  576. 

Cerebellum,  501,  ^02,  639,  640. 

Cerebral  hemispheres,  501,  502,  639,  640; 

vesicle,  397,  3QQ- 
Cerebratulus,  177,  178. 
Cerianthidea,  142;  Cerianthus,  142. 
Certhiid(B,  593. 

Cervid(B,  667,  669 ;  Cervus,  644,  669. 
Ceryle,  611. 
Cestoda,  150,  163-166. 
Cestus,  147. 
Cetacea,  633,  645. 
Chcstoderma,  252. 
ChcBlognatha,  180,  181. 
ChcBtopoda,  215,  232,  233-236. 
Ch(Btura,  613. 
ChalcididcB,  365. 
Chamceida,  591. 
Chamceleon,  537,  550,  551;    Chanudeon- 

tidcB,  537,  550- 
Chameleons,  527,  536,  537,  55o-55i- 
Chamois,  669,  671. 
CharadriidcB,  590,  607;    Charadriiformes, 

590,  607. 
Chary  bdea,  133. 
Cheetah,  656. 
Cheiropterygium,  446. 
Cheliceraj,  372,  373,  378. 
Cheliped,  278,  280. 
Chelonia,  527,  534,  543,  544;   Chelonidce, 

535;     CheloniidcB,    535;     Cheloniidea, 

535,  543. 
ChdydidcB,  536,  545. 
Chelydra,  530,  535,  540,  541 ;  Chelydridce, 

534,  540. 


Chemotropism,  36 ;  in  Ameba,  37 ;  cray- 
fish, 291 ;    earthworm,  228. 

Chcrnelidia,  382. 

Chevrotain,  667,  671. 

Chiggers,  380. 

Chilomonas,  45. 

Chihpoda,  310-31 1. 

ChimcRra,  431 ;  ChimcBridce,  431. 

Chimpanzee,  665,  666. 

Chipmunk,  658,  659. 

Chiromyidce,  662. 

Chironccles,  648. 

ChironomidcB,  357. 

Chiroptera,  642,  650-651. 

Chi  tin,  3. 

Chiton,  252;  Chitones,  251,  252. 

Chlamydosaurus,  553. 

Chlorogogen  cells,  216,  219. 

Choanocytes,  94. 

Choanoflagellata,  47. 

Chondrostei,  443,  452-454,  474,  695. 

Chondrotus,  511. 

Chordata,  24,  25,  386-413,  691. 

Chorion,  682. 

Choroid,  412. 

Chorophilus,  512,  519,  520. 

Chromatin,  13,  16-17. 

Chromatophores,  42,  43,  448,  522. 

Chromosomes,  15,  16;  in  fertilization, 
83,  85 ;  oogenesis,  82,  83 ;  reduction 
of,  85  ;   spermatogenesis,  81,  82.    • 

Chromotropjsm,  36. 

Chrysalis,  324. 

Chrysemys,  535,  541,  542. 

ChrysochloridcB,  650. 

ChrysomelidcB,  362. 

Chrysopa,  349, 

Chrysothrix,  664. 

Chyle,  323. 

Chyme,  319. 

Cicada,  346,  347,  348 ;   CicadidcB,  347. 

Cicindelida;,  360. 

Ciconiiformes,  590,  601. 

Cidaris,  190. 

Cilia,  53,  54,  134,  151,  178,  182. 

Ciliary  muscles,  412,  413, 

Ciliata,  62,  63,  64. 

CinclidcB,  591. 

Cinclides,  135,  136. 

Ciona,  391. 

Circulation,  Amphioxus,  398;  Anodonta, 
246;     Aster ias,    196;      crayfish,    278, 


INDEX 


709 


282-283;  earthworm,  221,  222;  honey- 
bee, 318,  319;   snail,  255;   squid,  266. 

Circulatory  system,  78;  Enteropneusta, 
388;  fish,  450;  frog,  484;  Hiriido, 
238;  lamprey,  418;  nemertine,  177, 
178;  perch,  438;  pigeon,  583,  584; 
rabbit,  638 ;  spider,  373,  374 ;  Squalus, 
425,  426;  turtle,  531;  vertebrates, 
406,  489. 

Circus,  605. 

Cirripedia,  294,  295,  299,  300. 

Cirrus,  of  A  mphioxus,  396, 397 ;  Planaria, 
152,  153. 

Citellus,  658. 

Civets,  653. 

Cladocera,  293,  294,  299. 

Clamatores,  616. 

Clams,  24,  263. 

Claspers,  of  dogfish,  423,  428. 

Class,  21 ;  Classification,  21-23. 

Clathrina,  104. 

Claudius,  535. 

Clavicle,  404,  495,  496. 

Clavicornia,  361. 

Claws,  372,  373,  403;  of  mammals,  677; 
of  Peripatus,  306,  307 ;  Pigeon,  577 ; 
poison,  of  centipedes,  310. 

Cleavage,  83,  85,  86,  87,  88,  507. 

Clemmys,  542. 

Clepsine,  232,  239. 

ClcridcB,  361. 

Clione,  258.  ^ 

Clisiocampa,  354. 

Clitellum,  217. 

Clitoris,  641. 

Cloaca,  154,  206,  207,  406,  481,  490. 

Clonorchis,  162. 

Clupea,  458,  459;  ClupeidcB,  444,  458; 
Clupeiformes,  443. 

Clypeus,  313. 

Clytia,  128. 

Cnemidophorus,  538. 

Cnidoblast,  no,  iii. 

Cnidocil,  no,  iii. 

Coagulation,  of  protoplasm,  11. 

Cobra,  539,  565. 

Coccida,  347. 

Coccidiidea,  52  ;  Coccidium,  52. 

Coccinellida,  363. 

Coccus,  370. 

Cochlea,  411,  640. 

Cockatoo,  591,  610. 


Cockroaches,  343. 

Cocoons,  155,  227,  228,  324. 

Codfish,  470,  474,  476. 

(^(ecilia,  510;  Cceciliidcs,  510,  512. 

Ccelenterata,  108-144;  classification,  108; 
contrasted  with  Qeno^/wra,  148;  defi- 
nition, 142  ;  economic  importance,  144, 
morphology,  142 ;   physiology,  143. 

Ccelenteron,  120. 

Ccelom,  88,  89;  Acanthocephala,  180; 
Amphioxus,  399;  Annelida,  240; 
Ascaris,  171,  172;  Asterias,  192,  210; 
Bugula,  184;  crayfish,  216,  217; 
Enteropneusta,  387,  388;  frog,  507; 
mollusks,  270;  nemertine,  177;  verte- 
brates, 401. 

Coelomata,  241. 

Coelomocoda,  25. 

Coelo  plana,  167. 

CoendidcE,  658,  666. 

Ccenolestes,  642,  648. 

Coenosarc,  120. 

Coenurus,  168. 

CoerebidoR,  593. 

Coleoptera,  337,  360-364. 

Coleps,  63. 

Colinus,  606. 

Collar,  cell,  94. 

CoUoblasts,  146,  147. 

Colon,  638. 

Colonial  Hydrozoa,  119,  120. 

Colors,  of  Amphibia,  522;  birds,  621. 

Colpoda,  63. 

ColubridcE,  539,  560;  Colubrina,  539. 

Columba,  575,  630 ;  Columbidce,  590,  607, 
609. 

Columella,  of  coral  polyp,  137 ;  frog,  505. 

Colymbiformes,  589,  599.  , 

Comb  jellies,  23,  145. 

Commensalism,  106. 

Condor,  604. 

Condylura,  642. 

Coney,  645. 

Conjugation,  59. 

Conuropsis,  610. 

Convolutions,  of  brain,  639. 

Coot,  606. 

Copepoda,  294,  295,  299,  300. 

Copperhead  snake,  566. 

Copulation,  crayfish,  288;  earthworm, 
226,  227,  228. 

Coraciiformes,  591,  610;   Coraciidee,  591. 


7IO 


INDEX 


Coracoid,  404,  495,  496. 

Cor  allium,  139,  140. 

Corals,  137,  139,  140. 

Coregomis,  459-460. 

CoreidcE,  348. 

CorisidcB,  348. 

Cormorant,  590,  601,  602. 

Cornea,  285,  412. 

Corpuscles,  406,  484,  638. 

Corrodentia,  337,  341. 

Corvidm,  591. 

Corydalis,  349. 

Costa,  333. 

Costata,  512,  522. 

Cotingidce,  591,  616. 

Cottontail,  658. 

Cougar,  656. 

Courlan,  607. 

Cowbird,  625. 

Coxa,  314,  315,  372. 

Coxopodite,  280. 

Coyote,  653,  654. 

Crabs,  275,  298,  302 ;  horseshoe,  383. 

Cracida,  606. 

Crane,  590,  607. 

Cranial  nerves,  409,  427. 

Cranium,  403,  436,  493,  494. 

Crappie,  467. 

Craspedote  medusae,  123,  129. 

Crayfish,  276-292  (see  Cambarus). 

Creeper,  593. 

Crepidula,  258,  260,  272. 

Cretaceous  period,  697. 

Crickets,  344,  345. 

Crinoidea,  208-210,  213. 

Cristivomer,  460. 

Crocodiles,  527,  536,  547,  548,  549;   skin 

of,  571. 
CrocodilidcB,  536,  548;    Crocodilini,  527, 

536,    547-549,   694,    695;     Crocodilus, 

536,  547-549- 
Crop,  earthworm,  218,  219;  pigeon,  576, 

583. 
Crossopterygii,  443,  452,  47i,  474,  695- 
Crolalince,  539;   Crotalus,  539,  568-569. 
Crow,  591. 

Crustacea,  275,  276-305. 
CryptobranchidcB,  511,  514;    Cryptobran- 

chus,  511,  514,  515. 
Cryptoccphala,  236. 
Cryptodira,  534. 
Crypturijormes,  589,  596. 


Ctenidia,  248. 

Ctenocephalus,  359,  360. 

Ctenophora,  145-149;  definition,  148. 

Cteno  plana,  167. 

Cubitus,  333,  334. 

Cubomeduscc,  133. 

Cuckoo,  591,  610,  625. 

Cucujidcs,  361. 

CuculidcB,  591,  610;    Cuculijormes,  590, 

610. 
Culcita,  189. 

Culex,  50,  331,  332,  357;  CulicidcB,  356. 
Cumacea,  294,  296. 
Cunina,  128. 
Cunocanlha,  128. 
Curlew,  590,  607. 
Cuscus,  642. 
Cuspidaria,  262, 
Cuticle,  Ascaris,  171,  172;    earthworm, 

216,   217;    Euglena,  43;    Hydra,   109, 

110;    liver  fluke,    158;    Paramecium, 

53;   Rotijera,  181,  182. 
Cyanea,  141. 
Cyanocitta,  615. 
Cyclas,  262. 
Cyclops,  294,  295,  300. 
Cyclosis,  55. 

Cyclostomata,  400,  414-421,  694,  695. 
Cygnina,  603;  Cygnus,  631. 
Cyllene,  363. 
Cynipidce,  366. 
Cynocephalus,  644. 
Cynomys,  658. 
Cynthia,  393, 
CyprinidcB,  443,  456-457 ;  Cypriniformes, 

443;  CyprinincB,  443,  456;  Cyprinus, 

457- 
Cypris,  293,  294. 
Cysticercus,  164,  165. 
Cystignathidce,  512,  520. 
Cystoflagellata,  48. 
Cytoplasm,  12,  13,  14. 

Dactylozooid,  125,  127. 
Daddy-long-legs,  379. 
Daphnia,  293,  294,  300. 
Dasyatis,  430. 

Dasyures,  649;  DasytiridcB,  649. 
Decapoda,  265,  268,  297,  301. 
Deer,  644,  667,  669. 

Delphinus,    645,   674,    675;     Delphinap- 
teridcE,  674;    Delphinidce,  674. 


INDEX 


711 


Demodex,  381. 

Demospongice,  105. 

Dendroccelum,  151,  156. 

Dendrocionus,  364. 

Dendronotiis,  261. 

Dcnisonia,  539. 

Dcntalium,  261. 

Dentary,  494. 

Denticeti,  645,  674. 

Dentine,  635,  678. 

Dentition,    acrodont,    553 ;    heterodont, 

679;   horaodont,  679. 
Dermal  branchicc,  192 ;    denticles,  424 ; 

papillae,  677 ;    plates,  677. 
Dcrmanyssus,  380. 
Dcrmalemydidce,  535,  540;    Dermatemys, 

535- 
DcrmestidcB,  361. 
Dermis,  402,  403,  479. 
Dermochelyidce,  535,  544. 
Dermophis,  510. 
Dertnoptera,  642. 
Dero,  236. 

Desmognathus,  511,  517. 
Development,    Asterias,    197;     Aurelia, 

131,      132;      echinoderms,     210-211; 

crayfish,  288;  frog,  506-510;  Gonione- 

mus,  124;    liver  fluke,  159;    lamprey, 

419;   mammals,  680-682;   perch,  441; 

Planaria,  154. 
Devonian  period,  697. 
Diapheromera,  344. 

Diaphragm,  honeybee,  320;  rabbit,  637. 
Diaptomus,  294. 
Diastylis,  294,  296. 
Dibranchia,  268. 
Dicotyles,  644. 

Dicyema,  176;  Dicyemidce,  176,  177. 
Didelphia,  632,  642;    Didelphiidce,  647; 

Didelphis,  642,  647. 
Didinium,  54. 
Diemyctylus,  511,  515. 
■Difflugia,  ig. 
Digetiea,  161. 
Digestion,  Ameba,  30;  coelenterates,  143  ; 

Grantia,g6;  Hydra,  113;  Paramecium, 

55. 
Digestive  system,  77;    Amphioxus,  396, 

397;    crayfish,   282;    Ctenophora,   146, 

147;    dogfish,  425;    earthworm,    220; 

frog,  480;    honeybee,  318;    lamprey, 

416,417;  leech,  238;  liver  fluke,  157, 


158;  perch,  437;  Peripatus,  307; 
pigeon,  583 ;  Planaria,  152 ;  snail, 
253;  spider,  373,  374;  squid,  265, 
266;  starfish,  194;  turtle,  530;  ver- 
tebrates, 405. 

Digit,  576,  581,  582. 

Digitigrade,  653. 

Dik-dik,  669. 

Dimorphism,  126,  621. 

Dinoflagellata,  47,  48. 

Dinornis,  589;  Dinornithiformes,  589, 
597. 

Dinosauria,  573. 

Diodont  466;  DiodontidcB,  466. 

Dioecious,  80. 

Diomedca,  590,  600. 

Diphycercal,  447. 

Diploblastic,  89. 

Diplocardia,  215,  236. 

Diplodiscus,  162. 

Diplopoda,  309-310. 

Dipnoi,  432,  445,  471-472,  474,  694,  695. 

Dipper,  591. 

Diprotodontia,  642. 

Diptera,  337,  356-359- 

Dipylidium,  166. 

Discoglossidce,  512,  522;  Discoglossus, 
512. 

Discomedusce,  130,  133. 

Discorbina,  41. 

Dis psadomorphincB,  539,  564. 

Dissimilation,  31. 

Dissosteira,  345. 

Distalia,  404. 

Distira,  539, 

Distomtim,,  162. 

Distribution  of  animals,  6-7. 

Dog,  643,  653,  684. 

Dogfish-shark,  422-428. 

Dolichoglossus,  387. 

Dolichonyx,  615. 

Dolphin,  64s,  674. 

Domesticated,  birds,  630-631 ;  mammals, 
684-685. 

Donkey,  671. 

Doris,  258. 

Dorsal,  pores,  217;  vessel,  318,  319. 

Dotterel,  607. 

Dove,  mourning,  609. 

Dowitcher,  607. 

Down,  577,  578. 

Draco,  537,  553. 


712 


INDEX 


DrassidcB,  377. 

Drepanidolcenia,  166. 

Drommdce,  596;   Dromceus,  589,  596. 

Drotnatherium,  685. 

Dromedary,  671. 

Drone,  honeybee,  312. 

Duckbill,  642,  646. 

Ducks,  590,  603,  630. 

Dugong,  64s,  673. 

Duodenum,  481,  576,  583,  638. 

Duplicidentata,  643. 

Dynastes,  328,  362. 

Dytes,  589. 

Dytiscidce,  360;  Dyiiscus,  332. 

Eagles,  590,  603,  605. 

Ear,  frog,  505;  perch,  440;  rabbit,  640; 
of  vertebrates,  410-41 1. 

Eardrum,  640. 

Earthworm,  215-231  (see  Lumbricus). 

Earwig,  342. 

Ecdysis,  288. 

EcheneididcB,  444,  467. 

Echidna,  642,  646. 

Echuiarachnius,  190,  205. 

Echinococcus,  168. 

Echinodermata,  189-214,  691,  693;  clas- 
sification, 189;  development,  210; 
parthenogenesis,  212;  systematic  po- 
sition, 213. 

Echinoidea,  189,  202-205. 

Echinopluteus,  211. 

Echinorhynchus,  180. 

EchinosphcErites,  209. 

Echinus,  203,  204. 

Echiuroidea,  187  ;  Echiurus,  187. 

Ecology,  26. 

Economic  importance  of,  Amphibia,  526; 
birds,  626-630;  clams,  etc.,  251,  263; 
coelenterates,  144;  earthworm,  230; 
echinoderms,  198,  208;  fish,  442,  474- 
476;  flatworms,  168;  insects,  370- 
371;  lamprey,  420;  mammals,  688- 
690;    reptiles,  570-571. 

Ectoderm,  88,  89. 

Ectoparasites,  161. 

Ectopistes,  609. 

Ectoplasm,  28. 

Ectoprocta,  184. 

Ectosarc,  28,  43,  53. 

Edentata,  643,  660-661. 

Edwardsiidea,  141. 


Eel,  444,  463,  S14. 

Egestion,  30. 

Eggs  of,  Ascaris,  171;    birds,  625;    Vol- 

vox,  46,  47. 
Ejaculatory  duct,  322. 
Eland,  669. 
Elanoides,  605. 
Elaphe,  539;   Elapince,  539,  564;   Elaps, 

539,  562,  564. 
Elasmobranchii ,  400,  422-431,  694,  695. 
Elateridce,  361. 
Electrotropism,  36,  58. 
Elephantiasis,  174. 
Elephants,  645,  672,  673. 
Elephas,  645,  672. 
Elk,  669. 

ElopidcB,  444,  458. 
Elytra,  334. 
EmballonuridcB,  651. 
Embole,  272. 

Embryology,  26,  85-89  (see  development). 
Emeu,  589,  596. 
Emyda,  536. 
Emys,  535,  542. 
Enamel,  635,  678. 
Encystment,  42,  44,  49,  50. 
Endolymph,  410. 
Endopodite,  276,  277,  279. 
Endosarc,  28,  43,  53. 
Endoskeleton,  391,   392,  403,  435,  436, 

437. 
Engy stoma,  512,  521 ;  Efigystomatida,  512, 

521. 
Entameba,  70. 
Enter ocoela,  25. 

Enteropneusta,  386-389,  691,  692. 
Enter ozoa,  25. 

Entoderm,  88,  89,  109,  no,  in. 
Entomostraca,  299-300. 
Entoparasites,  i6r,  165. 
Entoprocta,  184. 
Eocene  period,  686,  697. 
Eohippus,  699,  700. 
Eolis,  260. 
Epanorthid(B,  648. 
Epeira,  373,  375 ;  EpeiridcB,  377. 
Epemys,  660. 
Ephemerida,  337,  338. 
Ephyra,  131,  132. 
Epibdclla,  161. 
Epibole,  272. 
Epicoracoid,  495,  496. 


INDEX 


713 


Epicrates,  539. 

Epidermis,  402,  403,  479. 

Epididymis,  640. 

Epiglottis,  638. 

Epigynum,  373. 

Epihippus,  700. 

Epimeron,  276,  277,  329,  330, 

Epipharynx,  313. 

Epiphragm,  259. 

Epipodite,  277,  279. 

Episternum,  329,  330,  495,  496. 

Epitheliomuscular  cells,  109. 

Epithelium,  74,  75,  89. 

EquidcB,  671 ;  Eqiiiis,  644,  671,  684,  701. 

Eremias,  538. 

Erethizon,  643,  660. 

ErinaceidcB,  650;  Erinaceus,  642. 

Eristalis,  359. 

Erythrocytes,  484. 

Esocidce,  444,  462 ;  Esociformes,  444 ; 
Esox,  462. 

Ethmoid,  494. 

Eudendrium,  128. 

Eudyptes,  599. 

Euglena,  41-45  ;  anatomy,  42,  43  ;  be- 
havior, 43  ;  physiology,  43 ;  reproduc- 
tion, 42,  44. 

Eulamellibranchia,  262. 

Eumeces,  538,  557. 

Eumenidce,  364,  367. 

Eunectes,  559. 

Eupagurus,  297,  302. 

Etiphausiacea,  297. 

Euplectella,  103,  105,  106. 

Euplexoptera,  337,  342. 

Eicpomotis,  467. 

Eurypaiiropus,  309. 

Eurypteridce,  384 ;  Eurypterus,  384. 

Euspongia,  103,  105,  106. 

Eiitheria,  632,  642. 

Eulhrips,  342. 

Euthyneiira,  258. 

Euvanessa,  352. 

Evolution,  8;  of  horse,  698-701. 

Excretion,  20;  \n  Anieba,  sx  ;  ccelenter- 
ates,  143;  Grantia,  96;  starfish,  193, 
196.  » 

Excretory  system,  78,  440;  Amphioxus, 
399;  Ascaris,  170,  172;  crayfish,  284; 
earthworm,  223  ;  frog,  490-491 ;  honey- 
bee, 320;  leech,  239;  liver  fluke,  157; 
millipede,  310;    mussel,  248;    nemer- 


tine,  177,  178;  pigeon,  586;  Planaria, 
153;  Peri  pat  us,  307,  308;  rabbit,  639; 
rotifer,  182 ;  snail,  256 ;  spider,  373, 
675;  tapeworm,  164 ;  vertebrates,  407. 

Exoccipitals,  493,  494. 

Exocceiidce,  444,  463;  Exoccetus,  463. 

Exopodite,  276,  277,  279. 

Exoskeleton,  of  crayfish,  277 ;  honey-bee, 
312;   perch,  434;   vertebrates,  403. 

Expiration,  451,  452,  639. 

Exumbrella,  123. 

Ej^e,  411-413  (see  sense  organs);  brush, 
314,  315- 

Eyelid,  413,  441,  505. 

Eye-spot,  of  Amphioxus,  397,  399;  Eu- 
glena, 42,  43;  Planaria,  151,  152; 
starfish,  195,  197. 

Facet,  286. 

Faeces,  55,  406. 

Falco,  604 ;    FalconidcB,  590,  603 ;    Fal- 

coniformes,  590,  603. 
Fallopian  tube,  641. 
Family,  22. 

Fasciola  hepatica,  157,  158-161. 
Fat,  II ;  -body,  490,  492. 
Feathers,  577-579,  595,  627. 
Feet,  of  birds,  618,  619. 
Felida,  652,  656;   Felis,  643,  656,  685. 
Femur,  314,  315,  372,  404,  497. 
Ferce,  643. 

Fertilization,  47,  61,  80,  83-85,  586. 
Fibrin,  484. 
Fibula,  404. 
Fibulare,  404,  497. 
Filaria,  174;  FilariidoR,  174. 
Filibranchia,  262. 
Filoplumes,  577,  578. 
Fin,  of  Amphioxus,  394;   of  fishes,  445- 

448;  dogfish,  424;  lamprey,  414,  415; 

squid,  265,  266. 
Finch,  593. 
Fish,    basket-,    201 ;     cave-,    444,    462  ; 

cod-,    444,    470;     deep-sea,    472-473; 

devil-,  269 ;  dog-,  454,  455 ;  flat-,  476 ; 

flying,  444,  463  ;  fossil,  474 ;  hag-,  414, 

419,   420;    jew-,   446;     paddle-,   443, 

452-453  ;  pipe-,  444 ;  porcupine-,  466 ; 

saw-,  429;    sucking,  467;    sun-,  444; 

sword,  469. 
Fission,  n6,  136. 
Fissipcdia,  643,  652. 


714 


INDEX 


Flagellata,  45. 

Flagellum,  42,  43. 

Flame  cell,  153. 

Flamingo,  590,  602. 

Flatworms,  150-168. 

Fleas,  337,  359-360;    beach,  296,   301; 

cat  and  dog,  360 ;  human,  360 ;  jigger, 

360;   rat,  360;    snow,  338;  water,  299, 

300. 
Flicker,  614. 

Flight,  of  birds,  621-622. 
Flounder,  444,  469,  470. 
Fly,  337,  356-359;  bee,  358;  black,  357; 

blow,  358;    bot,  358,  359;    caddice-, 

350;     damsel-,    339;     dobson-,    349; 

dragon-,  339;  drone-,  359;    fire-,  361; 

fruit,  359;   Hessian,  357;   horse-,  358; 

house,  358,  370;  ichneumon,  364,  367; 

lace-wing,  349 ;  may-,  338 ;  saw-,  365 ; 

scorpion-,  349 ;  stone-,  340 ;  tsetse,  71, 

371. 

Flycatcher,  591,  615. 

Food,  29,  627-630  (see  digestive  system). 

Foot,  of  mollusks,  242,  244,  261,  264, 
26s,  270;   rotifers,  181,  182. 

Foramen  magnum,  493,  494. 

Foraminijera,  41. 

ForficulidcE,  342. 

Formicidcd,  364,  369. 

Fossil,  Amphibia,  525;  birds,  592,  593; 
fish,  474 ;  mammals,  685-687  ;  rep- 
tiles, 572;  vertebrates,  696-701. 

Fox,  643,  651,  653. 

Fringillidce,  593. 

Frog,  477-510;  behavior,  506;  circula- 
tory system,  484;  development,  506; 
digestive  system,  480;  economic  im- 
portance, 526;  excretory  system,  490; 
external  features,  478;  glands,  492; 
muscular  system,  497;  nervous  sys- 
tem, 501 ;  reproductive  system,  491 ; 
respiratory  system,  482  ;  sense  organs, 
504;  skeleton,  492. 

Frogs,  512,  517,  519-522. 

Frontoparietals,  493,  494. 

Fulica,  606. 

FuliguUnce,  603. 

Fulmar,  600;  Fulmarus,  600. 

Funiculus,  184. 

Funnel,  146,  147,  264,  265,  397,  399. 

Fur,  bearers,  688;  seal,  657. 

Furcula,  580,  581. 


GadidcB,  444,  470;  Gadus,  470. 

Galerucella,  362, 

Gall,   -bladder,   406,   481;     -gnat,   356; 

plant,  366. 
Galleria,  327. 
Galliformes,  590,  606. 
Gallinula,  606. 
Gallus,  630. 
Gamasidce,  380. 
Gammarus,  297,  298,  301. 
Gannet,  601. 
Ganoids,  454,  694,  695. 
Garpike,  443,  454. 
GasterosteidcE,     444,     464;      Gasterostei- 

formes,  444;   Gasierosleus,  464. 
Gasterostomum,  162. 
Gastraia,  303. 
Gastric,  filaments,  131 ;  mill,  282 ;  pouch, 

130. 
Gastrophilus,  358,  359. 
Gastropoda,  242,  243,  252-261. 
Gastrovascular  cavity,  93,  109,  no,  120, 

123,  134,  135- 
Gastrozooid,  125,  127. 
Gastrula,  87,  88,  no,  116,  507,  508. 
Gavia,  589,  599;   Gaviidce,  599. 
Gavialidce,  536,  548;    Gavialis,  536,  547, 

548. 
Gazelles,  671. 

Geckos,  537,  552 ;   Geckonida,  537,  552. 
Gelasimus,  297,  298. 
Gelechia,  356. 
Gemmules,  98,  99. 
Genitalia,  330. 

Genital  pores,  217  (see  excretory  system). 
Genus,  22. 
Geodia,  105. 

GeomyidcB,  658 ;  Geomys,  643,  660. 
Geonemertes,  177. 
Geophilus,  311. 
Geotria,  420. 
Geotropism,  36,  57. 
Gephyrea,  186,  187,  188. 
Germ-cells,  46,  47,  73,  75- 
Germinal  disk,  441. 
Germ-layers,  88,  89,  507,  508. 
Geryonia,  122. 
Gestation,  641. 
Gid,  168. 

Gila  monster,  556,  571. 
Gill,   arches,   437,   508;  bars,  397,  398; 

covers,  433 ;    rakers,  437,  439. 


INDEX 


715 


Gill-slits  oi,Amphioxus,  397,  398;  Enter- 
opneusta,  387,  388;  dogfish,  424;  lam- 
prey, 414,  415;  tunicates,  390,  392; 
vertebrates,  401. 

Gills  of,  crayfish,  284;  Limulus,  383; 
Nereis,  235;  mussel,  24.8,  249;  squid, 
265,  266. 

Giraffa,  644;  giraffe,  644,  671 ;  Giraffidce, 
667. 

Gizzard,  576,  583. 

Glands,  calciferous,  218,  219;  cement, 
181,  182;  coxal,  375;  Cowper's,  640; 
cutaneous,  677;  digestive,  481;  duct- 
less, 450,  492,  638;  epidermal,  415; 
green,    278,    284;     infraorbital,    637; 

.  lachrymal,  413,  678;  lymph,  638; 
mammary,  403,  634,  678;  milk,  634; 
mucous,  403,  479 ;  oil,  403 ;  parotid, 
637;  perineals,  634 ;  poison,  317,  318, 
372,  373,  479,  525;  prostate,  154,  640; 
salivary,  254,  255,318,  319;  scent,  310, 
678;  sebaceous,  403,  677;  shell,  158, 
164,  165 ;  silk,  373,  337 ;  sublingual, 
637 ;  submaxillary,  637  ;  sweat,  403  ; 
thymus,  451,  492;  thyroid,  451,  492; 
vitelline,  158,  159;   yolk,  164,  165. 

GlauconiidcB,  538,  559;    Glaueonia,  538, 

55Q- 
Glenoid  fossa,  404,  495,  496. 
Glires,  643,  658. 
Globigerina,  41. 
Glochidium,  250. 
Glomerulus,  387,  388,  491. 
Glossina,  71. 
Glossobalanus,  387. 
Glottis,  481,  482,  638. 
Glycogen,  406,  482. 
Glyptodon,  687. 
Gnatcatcher,  591. 
Gnus,  669. 
Goats,  667,  669,  685. 
Goatsucker,  591,  610,  612. 
Gonad,  130,  131,  402. 
Gonangium,  119,  120. 
Goniobasis,  259. 
Gonionemus,  122,  123,  124. 
Gonodactylus,  299. 
Gonotheca,  119,  120. 
Gonycephalus,  53?.. 
poose,  590,  603,  630. 
Gopher,  pocket,  643,  658,  660. 
Gopher  us,  543. 


GordiidcB,  179;  Gordius,  179. 

Gorgonacea,  139,  140. 

Gorilla,  644,  665,  666. 

Goshawk,  604,  606. 

Graafian  follicle,  641. 

Grafting,  117,  118,  155,  230. 

Grampus,  645,  674.  , 

Granatocrinus,  209. 

Grantia,.  94-98. 

Grasshopper,  344,  345. 

Grebe,  589,  599,  600. 

Gregarina,  52;  Gregarinida,  52. 

GrillidcB,  345. 

Ground-hog,  659. 

Grouse,  606. 

Growth,  10,  32. 

Gruidcc,  590,  606,  607;   Gruiformes,  590, 

606;  Grus,  607. 
Gryllotalpa,  332. 
Gryllus,  344. 
Guano,  626. 
Guillemot,  609. 
Guinea-fowl,  631. 
Gull,  590,  607,  608. 
Gullet,  42,  43,  53,  55,  130,  134,  I3S. 
Gulo,  656. 
Gunda,  156. 
Gymnodactylus,  537. 
Gymnogyps,  604. 

Gymnophiona,  510;  Gymnopis,  510. 
Gypogeranidce,    590,    603 ;     Gypogeranus, 

604. 
Gyrfalcon,  604. 
Gyrinidce,  360. 
Gyrodadyliis,  161. 

Haddock,  470,  474. 

Haemal,  arch,  436;  spine,  436. 

Hoematopinus,  345,  346. 

Haemocoel,  282,  307,  320. 

Haemoglobin,  221,  406,  484. 

Ilcemopis,  239. 

H centos poridia,  52. 

Hair,  403,  632,  676. 

Hake,  470,  474. 

Ilalcampa,  141. 

Haliaelus,  605. 

Halibut,  470,  474. 

Halicore,  645. 

Ilalictus,  367. 

Ilaliotus,  258. 

Halters,  330. 


7i6 


INDEX 


HapalidcB,  662,  663. 

Haplomi,  444. 

Hare,  643,  658. 

Hartebeests,  669. 

Harvestmen,  379. 

Hawks,  590,  603,  604,  605,  606. 

Heart,  406,  485  (see  Circulatory  system). 

Hedgehog,  642,  650. 

Helicodiscus,  259. 

HeUophila,  354. 

Heliosphcera,  40. 

Ileliothis,  354. 

Heliozoa,  40. 

Uelix,  254,  257,  258,  271. 

Hellbender,  514,  515. 

Ilelminlhophis,  538. 

Helodcrma,  537, 556;  Helodermatida,  537, 
556. 

Ilelodrilus,  215. 

Hemerobius,  349. 

Hemibranchii,  444. 

Hemichorda,  386. 

Hemidactylus,  552. 

Hemiphradus,  512. 

Hemiptera,  337,  345-348. 

Hepatic  portal  system,  425, 426, 488,  489, 
638. 

Hermaphrodite,  80;  duct,  254,  257. 

Heron,  590,  601,  602. 

Herring,  443,  444,  458, 

HesperidcB,  351. 

Hesperornis,  588,  593,  594;  Hesperor- 
nithiformes,  588,  594. 

Heterocera,  351,  352-356. 

Heterocercal,  447. 

Heteroccela,  105. 

HeterocyemidcE,  176,  177. 

Heterodon,  562. 

Heteromera,  363. 

Heterometabola,  334. 

Heteromi,  444. 

Heteroplera,  348. 

Heterotricha,  63.  64. 

Hexaclinellida,  92,  105. 

Hibernation,  of  Amphibia,  524;  Mam- 
malia, 682-683. 

Hipparion,  701. 

Hippobosca,  359. 

Hippocampus,  465. 

Hippoglossus,  470. 

Hippopoiamidce,  667 ;  Hippopotamus, 
644,  671.^ 


Hirudinea,  215,  232,  236,  237-239; 
Hirudo,  237-239. 

Uirundinidce,  591 ;   Ilirundo,  615. 

Histology,  26,  loi. 

Hoactzin,  590. 

Holoblastic  egg,  86. 

Holocene  Period,  686. 

Holocephali,  430-431,  471,  694. 

Holometabola,  335. 

Holophytic  nutrition,  43. 

Holostei,  443,  454-455,  474- 

Hololhuria,  190. 

Holothurioidea,  190,  205-208. 

Holotricha,  63. 

Holozoic  nutrition,  43, 

HomalopsincB,  539,  563  ;  Homalopsis,  539. 

Homarus,  297,  303. 

HominidcE,  662,  666;  Homo,  644,  666, 
667,  696. 

Homocercal,  447. 

Homocosla,  105. 

Homologous  organs,  76,  91. 

Homoptera,  346-348. 

Honeycomb,  325. 

Honey-bee,  312-328;  activities  of 
workers,  325-328;  circulatory  system, 
319;  digestive  system,  318;  excretory 
system,  320;  external  features,  312- 
318;  nervous  system,  320;  reproduc- 
tion, 322-324;  respiration,  320;  sense 
organs,  321. 

Honey-sac,  318. 

Hoofs,  403,  677. 

Hormiphora,  146,  148. 

Horn,  677. 

Hornbill,  610. 

Hornet,  368. 

Horse,  644,  671,  684. 

Humerus,  404,  495,  496. 

Humming-bird,  591,  611,  612-613. 

Humor,  aqueous,  412;  vitreous,  412. 

Hyoemoschus,  671. 

HycBna,  643,  653;  Hycenidce,  653. 

Hyas,  297. 

Hydatides,  168. 

Hydatina,  182. 

Hydra,  108-118;  morphology,  109; 
physiology,  112;  regeneration,  117; 
reproduction,  115. 

Hydr  actinia,  128. 

Hydranth,  119,  120. 

Hydra-tuba,  131,  132. 


INDEX 


717 


Hydrince,  539,  564. 

Hydrobatidce,  348. 

Hydrocaulus,  119,  120. 

IlydrocorallincB,  129. 

Hydroid  compared  with  medusa,  124. 

Hydrophilidoe,  361. 

Hydro  phis,  539. 

Ilydrophyllium,  125,  126. 

Hydrorhiza,  119. 

Hydrotheca,  119,  120. 

Hydrozoa,  108,  118-129;  classification, 
128;  metagenesis,  122;  polymor- 
phism, 126;   reproduction,  127. 

Hyla,  512,  519,  520;  Hylidce,  512,  519- 
520. 

Hylobates,  665. 

Hylodes,  512. 

Hymenolepis,  166. 

Hymenoplera,  337,  364-369. 

Hyoid  arch,  425,  437,  493,  494. 

Hyperbranchial  groove,  395,  396. 

Hyperparasitism,  7, 

Hyphantria,  353. 

Hypohippus,  701. 

Hypopachus,  512. 

Hypophysis,  417,  419,  501,  502. 

Hypostome,  no,  120,  121. 

Hypotricha,  64. 

Hypsirhina,  539. 

HyracoidcB,  645 ;  Hyrax,  645. 

Hyracotherium,  699,  700. 

IbididcE,  590;  Ibis,  590,  601. 

I  eery  a,  347,  363. 

Ichneumonidce,  364. 

Ichthyobdella,  239. 

Ichthyomyzon,  420. 

Ichthyophis,  510,  513. 

Ichthyopterygium,  446. 

Ichthyornis,     589,     594;      Ichthyornithi- 

formes,  589,  594. 
Ichtkyosaum,s73;  Ichthyosaurus,  573. 
Ictalurus,  458. 
I  derides,  593. 
Idyia,  145. 
Iguana,  537,  554,    571;    Iguanidce,  537, 

554. 
Ileum,  484. 
Ilium,  404,  495,  496. 
Imago,  323. 
Incisor,  635,  936,  679. 
Incubation,  586,  626. 


Infundibulum,  146,  147,  501,  502. 

Infusoria,  27,  62,  63,  64,  65,  71. 

Ingestion,  29,  30. 

Ink  sac,  265,  266. 

Irtsecta,  275,  312-371;  anatomy  and 
physiology,  328-336;  classification, 
336-337;  economic  importance,  370- 
371;   review  of  orders,  337-369. 

Insectivora,  642,  649-650,  696. 

Inspiration,  451,  639. 

Integument,  402,  403,  676-678. 

Intermedium,  404,  496,  497. 

Intermuscular  bones,  436, 

Interspinal  bones,  437. 

Interstitial  cells,  log. 

Intervertebral,  discs,  636;  ligaments,  636. 

Interzonal  fibers,  15,  16. 

Intestine  (see  digestive  system). 

Introvert,  188. 

Intussusception,  10. 

Invertebrates,  i,  691. 

Iridocytes,  448. 

Iris,  412. 

Irritability,  10,  19. 

Ischium,  404,  495,  496. 

Isopoda,  296,  297,  301. 

Isoptera,  337,  340. 

Isospondyli,  443, 

Ixodidce,  380. 

Jacana,  607,  608;  Jacanidce,  607,  608. 

Jaeger,  608. 

Jaguar,  656. 

Jay,  591- 

Jellyfish,  122,  123,  124. 

Julus,  309,  310. 

Jungle-fowl,  630. 

Jurassic  Period,  697. 

Kangaroo,  642,  648. 

Karyosome,  13.  ' 

Katabolism,  19,  29,  31. 

Keratosa,  105. 

Kidney,  401,  402  (see  excretory  organs). 

Kingbird,  615. 

Kingfisher,  591,  610,  611. 

Kinglet,  591. 

KinosternidcE,  Kinosternon,  535,  541. 

Kite,  603,  605. 

Kittiwake,  608. 

Kiwi,  589,  598. 

Kosnenia,  382. 


7i8 


INDEX 


Labial  palps,  245,  246,  313. 

Labium,  313,  372. 

Labyrinthodonts,  526. 

Lacerta,  538,  557;    Lacertidce,  538,  557; 

Lacertilia,  537. 
Lachesis,  539. 
Lachnoslerna,  362. 
Lacteals,  638. 
Lcemopsylla,  360. 
Lagomys,  643. 
Lagopus,  606. 
Lama,  671. 

Lamellibranchiata,  261. 
Lamellicornia,  361. 
Lampetra,  420,  421. 
Lamprey,  414,  415-420. 
Lampy ridce,.  s6i. 
Lancelet,  393,  394. 
Laniidce,  591.  • 

Laomcdea,  120. 
Lapwing,  607. 

LaridcB,  590,  607,  608 ;  Larus,  608. 
Lark,  591. 
Larva,  323,  324. 
Larvacea,  390,  393. 
Larynx,  482,  483,  639. 
Latax,  655. 

Lateral  lines,  172,  410,  415,  427. 
Zcffa,  262. 
Leech,  236. 

Lemming,  660,  683-684. 
Lemur,  644,  662,  663,  696;    Lemuridce, 

662,  696;   Lemuroidea,  644. 
Lens,  412. 
Leopard,  656. 
Lepas,  294,  300. 
Lepidoptera,  337,  350-3S6. 
Lcpidopleurus,  252. 
Lepidosiren,   472;     LcpidosirenidcE,   445, 

471- 
Lepidosternon,  538. 
Lepisma,  337,  338. 

Lepisosleidce,  443,  454;   Lepisosteus,  454. 
LePomis,  467. 

LeporidcB,  633,  658;  Lepus,  643. 
Leptinotarsa,  362. 
Leptocephalidce,  444. 
Leptodiscus,  48. 

Leptodora,  294.  ^ 

LeptomeduscE,  128. 
Leptoplana,  157. 
Lepius,  380. 


Leucocytes,  484. 

Leucosolenid,  92,  93,  94,  105. 

Liasis,  539.   • 

Libinia,  302. 

Life,  origin  of,  12;  succession  of,  697. 

Ligula,  313. 

Limax,  258,  259. 

Limicola,  236. 

LimnobatidcB,  348. 

Ximpet,  258. 

Limtdus,  383. 

Linguata,  512,  518-522. 

Lingula,  186. 

Linin  fibers,  13. 

Linyphiada,  377. 

Lion,  643,  656. 

Liriope,  122,  128. 

Lilhobius,  310,  311. 

Lithodyics,  520,  521. 

Littorina,  258. 

Liver,  246,  247,  401,  402,  438,  481. 

Liver  fluke,  157. 

Lizards,  527,  536,  537,  551-557- 

Llama,  667,  671. 

Lobosa,  39. 

Lobster,  301,  303. 

Locomotion  (see  Behavior). 

Locust,  344,  345  ;  Locustida,  345. 

Loligo,  264-267. 

Loon,  589,  599- 

Lophiidce,  444,  468 ;  Lophius,  468.  • 

Lophobranchii,  444. 

Lophophore,  184.  186. 

Louse,  341,  345,  346,  359- 

Loxocemus,  539. 

Loxodonta,  645,  672,  673. 

Loxophyllum,  63. 

Lucanidce,  361. 

Liiccrnaria,  132. 

Lumbricus,  215-231;  behavior,  228; 
circulation,  221,  222;  digestion,  220; 
economic  importanc>j,  230;  excretion, 
223;  external  features,  216;  nervous 
system,  223,  224;  reproduction,  226, 
227;  respiration,  223;  sense  organs, 
226. 

Lung-books,  373,  374,  379- 

Lung-fishes,  471-472. 

Lungs,  401,  402  (see  respiratory  system). 

Lutra,  655. 

Lycosa,  376. 

LygcBidcB,  348. 


INDEX 


719 


Lygosoma,  538. 

Lymantridoe,  353. 

Lymncea,  160,  258,  259,  271. 

Lymph,  490. 

Lymphatic  system,  407,  638. 

Lynx,  656. 

Mahiiia,  538. 

Mackerel,  444,  468,  469,  474. 

Macrohdella,  239. 

Macrobiotus,  384. 

Macrochelys,  535,  540,  541. 

Macrodactylus,  362. 

Macrodrili,  236. 

Macromere,  272,  507,  508. 

MacropodidcB,  647  ;  Macro  pus,  642. 

MacroscelididcE,  650. 

Madra,  262. 

Madrepora,  142;  MadrePoraria,  137, 141. 

Madreporite,  190,  193,  200,  202,  203,  206, 

207. 
Magellania,  185. 
Malacobdella,  177. 
Malacoclemmys,  542. 
Maiacopterygii,  443. 
Malacostraca,  294,  301-302. 
Malaria,  50-52;  parasite  of,  50. 
Mallophaga,  337,  341. 
Malpighian,  body,  491 ;  tubule,  310,  311, 

318,  320,  373,  375- 
Mamtnalia,  401,  632-690,  694. 
Man,  644,  662  ;  races  of,  667,  696. 
Manatee,  645,  673;  Manatus,  645,  673. 
Mandible,  278,  279,  313. 
Man  is,  643,  661,  662. 
Mantidce,  343;  Mantis,  332,  343. 
Mantle,  of  moUusks,  242,  246,  247,  253, 

265,  270. 
Manubrium,  120,  121,  123. 
Margarita,  258. 
Margaropus,  380. 
Marmosa,  648. 
Marmoset,  662,  663. 
Marmota,  659. 

Marsupialia,  642,  647-649,  694,  696. 
Marsupium,  250.  ( 

Martens,  652,  655. 
Massasauga,  569. 
Mastax,  181,  182. 
Mastigameba,  45. 
Mastigophora,  41-48,  70, 
Mastodon,  687. 


Maturation,  81,  82,  83. 

Maxillae,  of  crayfish,  277,  279;   frog,  493, 

494;  honey-bee,  313;  perch,  436,  437; 
>  spider,  372. 
Maxilliped,  279,  280. 
Meandrina,  141,  142. 
Meanies,  511,  514. 
Mecopiera,  337,  349. 
Medulla  oblongata,  427,  501,  502. 
Medullary,  fold,  507,  508;   groove,  507, 

508. 
Medusa,  120,  121;  bud,  120,  121. 
Megachile,  366. 
Megachiroptera,  650. 
Megalobatrachus,  514. 
Meganyctiphanes,  297. 
Megaptera,  675. 

Melanoplus,  329,  336,  344,  345. 
Meleagris,  606. 
Meloidce,  363. 
Melophagus,  359. 
Melospiza,  615. 

Membranous  labyrinth,  410,  411. 
Menisccessus,  685. 
Menopon,  341,  342. 
Mentum,  313. 
Meniira,  617. 
Mephitis,  643,  655. 
Merganser,  603 ;  Mergina,  603. 
Meroblastic  egg,  86. 
Mesenteric  filaments,  135,  1-36. 
Mesentery,  132,  135,  136. 
Mesoderm,  88,  89,  148. 
Mesoglea,  109,  no. 
Mesohippus,  699,  700. 
Mesosoma,  378. 
Mesosternum,  495,  496. 
Mesothorax,  314. 
Mesozoa,  176-177. 
Mesozoic  Era,  697. 

Metabolism,  10,  19-20,  29,  55,  102,  270, 
Metacarpals,  404,  497'. 
Metagenesis,  80-81,  122. 
Metamere,  90. 

Metamerism,  90,  91,  240,  401. 
Metamorphosis,     of     insects,     334-336; 

tunicates,  392. 
Meta  phase  of  mitosis,  15,  16. 
Metaplasm,  13. 
Metapleural  fold,  394,  395. 
Metasoma,  378. 
Metatarsus,  372,  497. 


720 


INDEX 


Metatheria,  642. 

Metathorax,  314. 

Metazoa,  24,  25,  73-91. 

Metridium,  134,  135,  136,  141. 

Mice,  658,  660,  698. 

Micracidium,  159. 

Microcentrum,  344. 

Microdrili,  236. 

Micromere,  507,  508. 

Micronodon,  685. 

MicropodidcB,  591,  613. 

Microptenis,  467. 

Microsauria,  525,  526. 

Microstoma,  156. 

Micriira,  177. 

Midas,  663. 

Midges,  357. 

Migration,  of  birds,  622 ;  of  mammals,  683. 

Millepora,  129. 

Millipedes,  309-310. 

MimidcE,  591 ;  Mimus,  615. 

Mink,  655. 

Minnows,  443,  456. 

Miocene  period,  697. 

Mites,  381. 

Mitosis,  14,  15,  16. 

Mniotiltidce,  593, 

Moa,  589,  597- 

Modiola,  262. 

Molar,  636,  679. 

Moles,  642,  649,  650. 

Molgula,  393. 

Molluscoidea,  183. 

MolossidcB,  651. 

Molting,  288,  324,  578. 

Mollusca,  24,  25,  242-273 ;  classification, 
243,  272;  metabolism,  270;  mor- 
phology, 269;   reproduction,  271. 

Monaxonida,  105. 

Monitors,  537. 

Monkeys,  644,  662,  663,  664,  696. 

Monocystis,  48,  49,  50. 

Monodelphia,  632,  642. 

Monodon,  675. 

Monoecious,  80. 

Monogamous,  653. 

Monogenea,  161. 

MonopeUis,  538. 

Monops,  156. 

Monoscelis,  156. 

Monosiga,  47. 

Monostomum,  162. 


Monotremata,  642,  645-676,  694,  695,  696. 

Moose,  644,  669. 

Mordacia,  420. 

Morphology,  26. 

Mosquitoes,  50,  356,  357,  371. 

Motacillidce,  591. 

Moths,  328,  337,  338,  352-356. 

Motmot,  610. 

Mouse,  643. 

Mouth,  53  (see  digestive  system). 

Mouth  parts  of  insects,  313,  331. 

Mucosa,  481. 

Mud-puppy,  477,  510,  513. 

Mugiliformes,  444. 

Mullet,  444. 

Multituberculata,  685. 

Mungoose,  653.    » 

Murida,  658,  660. 

Murre,  609. 

Mils,  643,  660. 

Musca,  358;  Muscida,  358. 

Muscular  system,  78;    of  Ascaris,  172; 

crayfish,    287;     frog,    497,    498-501; 

lamprey,  416,  417;    liver  fluke,   157; 

Metridium,     135,     136;     perch,    437; 

pigeon,  582;    Planaria,  153;    starfish, 

192 ;   vertebrates,  405. 
Muscular  tissue,  74,  75. 
Muskallunge,  462. 
Musk-ox,  669,  670,  671. 
Muskrat,  660. 
Mussel,  243. 
Mustang,  701. 
Mustclida,  652,  655,  688. 
Mustdis,  431. 
Mutabilia,  511,  514-517. 
Mya,  262. 
Myodes,  660. 
My  Otis,  643,  651. 
Myotome,  394,  416,  417. 
Myriapoda,  275,  308-311 
Myrmecobiida;,  649. 
Myrmecocystus,  369. 
Myrmecophaga,  643,  661 ;  Myrtnecopha- 

gidce,  661. 
Mysidacea,  294. 
Mysis,  294,  296,  304. 
Mystacoceti,  645,  675-676. 
Mytilus,  262. 
Myxine,    414,     420;      MyxinidcB,     420; 

Myxinoidea,  420. 
Myxosporidia,  52. 


INDEX 


72t 


Nails,  677. 

Nais,  236. 

Naja,  539,  565. 

Narcomedusce,  128. 

Nares,  481,  482,  483. 

Nar whale,  674,  675. 

Nasals,  493,  494;  aperture,  415. 

NatalidcB,  651. 

Natantia,  297,  299. 

Matrix,  561. 

Nauplius,  289,  303,  304. 

Nautilus,  268,  269. 

Neanderthal  man,  696. 

Nebalia,  294,  295;  Nebaliacea,  294,  295. 

Necator,  175. 

Nectonema,  179. 

Nectophore,  125,  126. 

Necturus,  161,  511,  513. 

Nemathelminthes,  24,  25,  169-175. 

Nematocera,  356. 

Nematocysts,  109,  iii,  112,  131,  134. 

Nematomorpha,  179. 

Nematus,  365. 

Nemertinea,  177,  178,  179. 

Neoceratodiis,  446,  471. 

Neornithes,  575,  594. 

Neosporidia,  52. 

Nephridia,  216,  223  (see  excretory  sys- 
tem). 

Nephridiopore,  216,  217  (see  excretory 
system). 

Nephrocytes,  196. 

Nephrostome,  216,  223,  491. 

Nereis,  232,  233,  234-235. 

Nerves,  cranial,   408,  409;   spinal,  408. 

Nervous  system,  79;  central,  224,  408; 
peripheral,  224,  408;  sympathetic, 
408,  410. 

Nervous  system  of,  Amphioxus,  397, 
399;  Ascaris,  170;  crayfish,  278,  284 ; 
dogfish,  427;  earthworm,  223,  224, 
225,  226;  Enteropneusta,  387,  388; 
frog,  501-504;  Gonionemus,  123; 
honey-bee,  318,  320;  Hydra,  112; 
lamprey,  418 ;  liver  fluke,  157  ;  mussel, 
247,  249;  nemertine,  177,  178;  perch, 
440;  Peripatus,  307,  308;  pigeon, 
587;  Planaria,  152,  153;  rabbit,  639; 
snail,  256;  spider,  373,  375;  squid, 
267 ;  starfish,  195,  197 ;  tapeworm, 
164 ;  tunicate,  391 ;  turtle,  533 ;  ver- 
tebrates, 407,  408,  410. 


Nervous  tissue,  75,  76, 

Nervures,  333. 

Nests,  of  birds,  624-625. 

'Neural,  arch,  402,  404,  493,  495 ;   spine, 

404. 
Neurocoele,  386. 
Neuron,  225. 
Neuroptera,  337,  349. 
Newt,  515. 

Nictitating  membrane,  413,  505,  576. 
Night-hawk,  612. 
Noctilionidce,  651. 
Noctiluca,  48. 

Noctua,  332;  NoctuidcB,  354. 
Noddie,  608. 
Nose,  410. 
Nosema,  52. 
Nostril,  478. 
Notacanthiformes,  444. 
Notochord,    386;     of   Amphioxus,    396, 

397;      Enter  opneusta,    387;      dogfish, 

424;    lamprey,  416,  417;    perch,  435; 

tunicate,  390,  392 ;    vertebrates,  401 . 
NotonectidcB,  348. 
Notary ctidce,  649. 
Nototrema,  512,  520. 
Novius,  347,  363. 
Nucleolus,  13. 

Nucleus,  12,  13,  14,  15,  16,  17. 
Nucula,  262. 
Nudibranchs,  260. 
Numidea,  631. 
Nuthatch,  591. 

Nutrition,  112  (see  digestive  system). 
Nymph,  336,  338. 
NymphalidcB,  352. 

Obelia,  1 19-12 2. 

Obisium,  382. 

Ocapia,  671. 

Occipital  condyles,  493,  494,  579,  635. 

Ocelli,  131,  312,  313. 

Octopoda,  268,  269;  Octopus,  269. 

Oculina,  141,  142. 

OdobcenidcB,  657 ;  Odoboenus,  643,  657. 

Odocoileus,  669. 

Odonata,  337,  339. 

Odonioceti,  645,  674-675. 

(Ecodoma,  369. 

(Esophagus,  480  (see  digestive  system), 

CEstridce,  359. 

Oiko pleura,  393. 


3A 


722 


INDEX 


Okapi,  671. 

Olfactory,  capsule,  416,  418;  chamber, 
482,  483;  lobes,  501,  502;  pits,  131, 
397,  399;  sac,  440  (see  nervous  sys- 
tem and  sense  organs). 

Oligocene,  686,  697. 

OligochcBta,  236. 

Ommastrephes,  268. 

Ommatidium,  285,  286. 

Ommosternum,  495,  496. 

Omnivorous,  21. 

Oncorhynchus,  461. 

Oniscus,  296,  297,  301. 

Onithochiton,  252. 

Ontogenesis,  302. 

Onychophora,  275,  305-308. 

Oocytes,  82,  83,  84. 

Ocecium,  184. 

Oogenesis,  82,  83,  84. 

Oogonia,  82,  83. 

Opalina,  63. 

Operculum,  433,  439. 

Ophibolus,  562. 

Ophidia,  538. 

Ophioglypha,  200,  201. 

Ophiopluteus,  210,  211. 

Ophisaurus,  556. 

Ophiiira,  189. 

Ophiuroidea,  189,  199-201. 

Opisthobranchia,  258. 

Opisthocomidcd,  590. 

Opisthoglypha,  539,  563- 

Opossum,  642,  647,  648. 

Optic,  chiasma,  501,  502;  lobes,  501,  502 
(see  nervous  system) . 

Optinum,  in  behavior,  44,  57. 

Oral,  groove,  53 ;  hood,  396,  397 ;  lobe, 
123,  130;   papillae,  306. 

Orang-utan,  644,  665. 

Orca,  675. 

Order,  22. 

Oreamnos,  670. 

Organization,  9-10. 

Organs,  76 ;  analogous,  76 ;  homologous, 
76 ;  systems  of,  76-79. 

Origin  of  muscles,  497. 

Oriole,  593- 

Ornithorhynchus,  642,  646. 

Orohippus,  700. 

OrthonectidcB,  176,  177.  ' 

Orthoptera,  337,  343,  344,  345- 

Orycteropus,  644. 


Oscines,  616. 
Osculum,  93. 
Osmosis,  220. 
Osphradium,  249. 
Osprey,  605. 

Ossicle,  ambulacral,  191,  192. 
Ostariophysi,  443. 
Osteolxmus,  548. 
Ostia,  94,  135. 

Ostracoda,  293,  294,  299,  300. 
Ostrea,  262,  263. 
Ostrich,  589,  595,  596. 
OtariidcE,  657. 
Otoes,  657. 
Otter,  655. 

Ovary,  490, 491  (see  reproductive  system). 
Ovibos,  670,  671. 

Oviduct,  490,  492  (see  reproductive  sys- 
tem). 
Oviparous,  80,  413. 
Ovipositor,  330. 
Ovis,  670,  685. 
Ovum,  75. 
Ovotestis,  254,  257. 
Owl,  591,  611,  612. 
Ox,  684. 
Oxyglossus,  512. 
Oxyrhopus,  539. 
Oxytricha,  65. 
Oyster,  263,  271 ;  drill,  260. 

Pachyderms,  672. 

Pjedogenesis,  80. 

Palccmon,  289,  290. 

Palcemondcs,  297,  299,  301. 

Falceospondylus,  421. 

P.alamedcidcc,  590,  603. 

Palaptcryx,  597. 

Palate,  637. 

Palatine,  493,  494- 

Paleontology,  26. 

Paleozoic,  697. 

Palinurus,  297. 

Pallium,  246. 

Palp,  313. 

Palpigradi,  382. 

Pdludicola,  512. 

Paludina,  271,  272. 

Pan,  665,  666. 

Pancreas,  401,  402,  406,  481,  638. 

Pandion,  605. 

Pangolin,  643,  661,  662. 


INDEX 


723 


I 


Panorpa,  349. 

Panther,  656. 

Pantopoda,  385. 

Papilio,  352;  PapilionidcB,  351. 

Papula,  192,  193. 

Paradisea,  617. 

Paragonimus,  162. 

Parahippus,  701. . 

Paramecium,  53-62  ;  anatomy,  53  ;  be- 
havior, 55 ;  metabolism,  55 ;  repro- 
duction, 59. 

Paramenia,  252. 

Paramylum,  42,  43, 

Paramyxine,  420. 

PaYapodia,  233,  234,  235. 

Parapophysis,  435. 

Parapteron,  330. 

Parasites,  6,  7,  251. 

Parasitica,  345. 

Parasphenoid,  493,  494. 

Parazoa,  24,  25. 

Pareiopod,  278,  280. 

Parenchyma,  158. 

Parida;,  591. 

Paroquet,  610. 

Parrot,  591,  610. 

Parthenogenesis,  80,  212. 

Parthenogonidia,  46,  47. 

Partridge,  606. 

Passeriformes,  591,  614,  615. 

Patella,  372,  637  ;   Patella,  271. 

Pathogenic  Protozoa,  70-71. 

Pathology,  26. 

Pauropoda,  309 ;  Pauropus,  309. 

Pavo,  631. 

Peacock,  631. 

Pearls,  263,  264. 

Peccary,  644,  667,  668, 

Pecten,  588;  Pecten,  262. 

Pectinatella,  185. 

Pectines,  378. 

Pectinibranchia,  258. 

Pectoral  girdle,  404,  404  (see  skeleton). 

Pedicellaria,  191,  192,  203. 

Pedicellina,  185. 

Pediculidcc,  345  ;  Pediciilus,  345. 

Pedipalpi,  372,  378;  Pedipalpi,  381-382. 

Peduncle,  185,  186. 

Pelagia,  133. 

Pelecanidce,  590,  601. 

Pelccypoda,  242,  243,  261,  262,  263. 

Pelican,  590,  601, 


Pellicle,  53. 

Pelobates,  512;  Pelobatida,  512,  518-519. 

Pelomedusa,  535  ;   PelomedusidcB,  535. 

Feltogaster,  294. 

Pelvic  girdle,  404,  405  (see  skeleton). 

Pen,  265,  266. 

Penceus,  2g7,  303-305. 

Penguin,  589,  598,  599. 

Penis,  152,  322  (see  reproductive  system). 

Pennae,  578. 

Pennatula,  140;  Pennaiulacea,  140. 

Pentaceros,  199. 

Pentacrinus,  190,  209. 

Pentastomida,  384,  385;  Pentastomumf 
384. 

Pentatomidce,  348. 

PeramelidcB,  649. 

Perca,  432;  Percesoces,  444;  Percida, 
444,  467- 

Perch,  432-442,  467  ;  circulatory  system, 
438 ;  development,  441 ;  digestive 
system,  437;  excretory  system,  440; 
external  features,  432;  locomotion, 
433 ;  muscular  system,  437 ;  nervous 
system,  440 ;  reproductive  system,  441  ; 
respiratory  system,  438 ;  sense  organs, 
440;    skeleton,  434. 

Pericardium,  406  (see  circulatory  system). 

Peridinium,  47,  48. 

Perilymph,  410. 

Perinatal  pouch,  634. 

Periostracum,  245. 

Peripatus,  305,  306,  397,  308. 

Periphylla,  132,  133. 

Periplaneta,  331,  343. 

Periproct,  202,  203. 

Perisarc,  119,  120. 

Perissodactyla,  644,  671-672. 

Peristome,  191.  , 

Peritoneum,  193,  219,  479,  481.    ^^_„^ 

Peritricha,  65. 

Periwinkle,  260, 

Permian,  697. 

Peromedusce,  132,  133. 

Persa,  128. 

Petrel,  590,  600,  601. 

Petromyzon,  414,  415-420;  circulatory 
system,  417,  418;  development,  419; 
digestive  system,  416,  417;  economic 
importance,  420;  external  features, 
415;  muscular  system,  416,  417; 
nervous  system,  417,   418;    relation- 


724 


INDEX 


ships,  419;  respiratory  system,  417, 
418;  sense  organs,  417,  418;  skeleton, 
416;    urinogenital  system,  417,  419. 

Pelromyzontia,  420. 

PhalacrocoracidoR,  590,  601 ;  Phalacro- 
corax,  601,  602. 

Phalanger,  642,  649;   Phalangeridce,  649. 

Phalanges,  404,  497,  576,  582, 

Phalangidea,  379;   Phalangium,  379. 

Phalarope,  607. 

Phanerocephala,  236. 

Phaneroglossa,  512. 

Pharynx,  152,  157,  397,  405,  438,  638. 

PhascolomyidcE,  649. 

Phasianidce,  590,  606. 

Phasmidce,  343,  344. 

Phasmomantis,  343. 

Pheasant,  590. 

Philodina,  182. 

Philodryas,  539. 

Phoca,  643,  657 ;  Phocidce,  657. 

Phocoena,  645. 

PhoenicopteridcB,  590,  602  ;  Phoenicopterus, 
602. 

PhoUdota,  643,  661. 

Phoronidea,  185 ;  Phoronis,  185. 

Phosphorescent  organs,  473. 

Photosynthesis,  20-21. 

Phototropism,  36,  37,  38,  43,  229. 

Phryniscus,  512. 

Phrynosoma,  537,  555. 

Phthirius,  345. 

Phyllobates,  512. 

Phyltodactylus,  552. 

Phyllopoda,  292,  293,  299. 

Phyllostomida,  651. 

Phylloxera,  346. 

Phylogeny,  26,  302 ;  of  vertebrates,  693- 
696. 

Phylum,  21,  23-25. 

Physa,  258,  259. 

Physalia,  125,  126. 

Physeler,  675. 

PhyseteridcB,  674. 

Physiology,  26. 

Phytophaga,  362. 

Pia  mater,  504. 

Pica,  643. 

PicidcB,  591,  614. 

Pieridce,  352;  Pieris,  352. 

Pig,  667,  685;  guinea,  643. 

JPigeon,    575-588;    circulatory     system, 


583 ;  digestive  system,  583 ;  excretory 
system,  596;  external  features,  575; 
feathers,  577  ;  muscular  system,  582 ; 
nervous  system,  587;  reproductive 
system,  586 ;  respiratory  system,  585  ; 
sense  organs,  587 ;    skeleton,  579. 

Pike,  444,  462,  267,  475,  476. 

Pilidium,  178,  233. 

Pincher,  278,  280. 

Pinna,  411,  633,  640. 

Pinnipedia,  643,  652,  656. 

Pinnotheres,  297. 

Pinnule,  209,  210. 

Pipa,  512,  518. 

Piro plasma,  381. 

Pisces,  432-476,  694. 

Pithecanthropus,  666,  696. 

Pithecia,  664. 

Pituitary  body,  417,  419. 

Placenta,  641,  680,  681,  682. 

Placentalia,  642,  694,  696. 

Plagionotus,  363. 

Plague,  360,  371. 

Plaice,  469. 

Planaria,  150,  151-155. 

Plankton,  6. 

Planorbis,  258,  259. 

Plantigrade,  634. 

Planula,  104,  120,  121,  124. 

Plasmodium,  50^51,  52. 

Plasmosome,"t3. 

Plastids,  13,  14. 

Plastron,  528,  529. 

PlatanistidcB,  674. 

Plates,  of  sea  ui-chin,  202,  203. 

Platiirus,  539. 

Platyhelminthes,  23,  25,  150-168. 

Platypus,  646. 

Platysamia,  353. 

PlatysternidcE,  535;   Platysternum,  535. 

Plautus,  609. 

Piece ptera,  337,  340. 

Pleistocene,  686,  697. 

Pleopods,  277,  278,  281. 

Plethodon,  511,  517;   Plethodontida,  517. 

Pleurobrachia,  146. 

Pleurobranchia;,  284. 

Pleuron,  276,  277. 

Pleurocera,  259. 

Pleurodira,  535. 

PleuronectidcB,  444,  469-470. 

Pleurum,  330. 


INDEX 


725 


Pliohippus,  701. 

Plover,  590,  607. 

Plumatella,  185. 

Flumularid,  128. 

Pneumatophore,  125,  126. 

Podicipcdidce,  6cx). 

Podobranchiae,  284. 

Podocnemis,  535. 

Podophyra,  64,  65. 

Po'ephagus,  671. 

Polar  bodies,  82,  83,  84. 

Polian  vesicles,  193,  194. 

Polistes,  368. 

Pollack,  470,  474. 

Pollen,  basket,  315;  brush,  314,  315. 

Polyandry,  625. 

Polychceta,  234-236. 

PolychcBrus,  156. 

Polycladida,  156,  157. 

Polydesmus,  310. 

Polygamy,  657. 

PolygordiidcB,  232;  Polygordius,  232,  233. 

Polygyra,  258,  259. 

Polymorphism,  125,  126. 

Polyodon,   452-453;    Polyodpntida,  443, 

452. 
Polyp,  23. 
Polypide,  184. 
Polyplacophora,  251,  252. 
Polyprotodontia,  642. 
Poly pter idee,  443  ;   Polypterus,  447,  452. 
Polyscelis,  156. 
Polystomum,  161. 
Polyzoa,  183-185. 
Pomoxis,  467. 
Pongo,  665. 
Pontobdella,  239. 
PorcelUo,  297. 

Porcupine,  643,  658,  660;  fish,  444. 
Porifera,  23,  25,  92-107 ;    classification, 

104 ;     morphology,    99 ;     physiology, 

102  ;  position  in  animal  kingdom,  105  ; 

relations  to  man,  106. 
Porospora,  52. 
Porpoise,  645,  674,  675. 
Porthetria,  353. 

Portuguese  man-o'-war,  125,  126. 
Postscutellum,  330. 
Potomobius,  276. 
Praescutum,  330. 
Prairie-dog,  658. 
Prawns,  301. 


Prefl^ceous,  690. 

Prehallux,  497. 

Premaxilla,  436,  437,  493,  494. 

Premolar,  636,  679. 

Priapidoidea,      187,      188;      Priapulus, 

187. 
Primates,  632,  644,  662-667. 
Pristis,  429. 
Proboscidea,  645,  672. 
Proboscis,  of  Acanthocephala,  180 ;  Echiu- 

roidea,  187 ;  Enteropneusta,  387 ;  moths, 

332;    nemertine,  177,  178;    Planaria, 

151,  152. 
Procavia,  645. 
Procellaria,  590,  601 ;  ProcellariidcE,  600 ; 

Procellariiformes,  590,  600. 
Procoracoid,  404. 
Proctodseum,  508. 
Procyon,    643,    654;     Procyonida,    652, 

654- 
Proechidna,  646. 
Proglottides,  163,  164. 
Pronghorns,  667,  669. 
Prootics,  493,  494. 
Prophase  of  mitosis,  14,  15. 
Propolis,  326. 
Prosoma,  378. 
Prospalia,  365. 
Prosopyles,  95,  100. 
Prostomium,  216,  224. 
Proteid,  11. 
Proteida,  510,  513;    ProteidcB,  510,  511, 

513-514- 
Proteroglypha,  539,  564. 
Proterospongia,  47. 
Proteus,  511,  513. 
Prothorax,  314. 
Protobranchia,  262. 
Protocercal,  447. 
Protodonta,  685. 
Protodrilus,  232. 
Protohippus,  699,  701, 
Protoplasm,  9,  lo-ii. 
Protopodite,  276,  277,  279. 
Protopterus,  471,  472. 
Protorohippus,  699,  700. 
Prototheria,  633,  642. 
Protozoa,   23,   24,   25,   27-72 ;    behavior, 

68;  classification,  27 ;  morphology,  66 ; 

pathogenic,   70 ;    physiology,   67 ;    re- 
production, 69. 
Protozoaea,  303,  304. 


726 


INDEX 


Protracheata,  275. 

Proventriculus,  218,  219,  234,  335,  576, 

583. 
Psephurus,  452. 
Pseudobranchus,  511,  514, 
Pseudometamerism,  240, 
Pseudopleuronedes,  470. 
Pseudopodia,  28. 
Pseudoscorpionida,  382. 
Psittacidce,  591,  610;  Psitlacus,  610. 
Psocus,  341 . 
Psoroptes,  381. 
Psychology,  26. 
Ptarmigan,  606. 
Pteranodon,  574. 

PteropidcB,  650;  Pteropus,  643,  651. 
Pterosaur ia,  573, 
Pterygiophores,  437. 
Pterygoid,  493,  494. 
Pterylae,  578. 
Ptilodiis,  685. 
Piilogonatidce,  591. 
Ptinidce,  361. 
Pubis,  404,  495,  496. 
Puffin,  609;  Puffinus,  600, 
Pulex,  360. 
Pulmonata,  258. 
Pulp-cavity,  678,  679. 
Pulvillus,  316. 
Puma,  656. 
Pupa,  323,  324. 
Pupil,  412,  505. 
Pupipara,  356,  359. 
Putorius,  655. 
Pycnogonida,  384,  385. 
Pygostyle,  579,  580. 
Pyloric  stomach,  278,  282. 
Pyrosoma,  393, 
Python,   538,   539,   557,   559,   560;    Py- 

thonincB,  539. 

Quadratojugal,  493,  494. 
Quadruped,  633. 
Quail,  590,  606. 
Queen  honey-bee,  312. 
Quill,  577. 

Rabbit,  633-641,  658,  689;  circulatory 
system,  638;  digestive  system,  637; 
excretory  system,  639;  external  fea- 
tures, 633  ;  nervous  system,  639 ;  re- 
productive  system,    640;    respiratory 


system,  639 ;  sense  organs,  640 ;  skele- 
ton, 634. 

Raccoon,  643,  652,  654. 

Radiale,  404,  496,  497. 

Radiata,  213. 

Radiolaria,  40. 

Radio-ulna,  496,  497. 

Radius,  333,  404. 

Radula,.255,  270. 

Rail,  590,  606. 

Rallidce,  590,  606. 

Rallus,  606. 

Rana,  477,  512,  521,  522;  Ranidce,  512, 
521-522. 

Rangifer,  669. 

Rat,  643,  658,  660,  689. 

Rattlesnakes,  567-569. 

Rays,  429,  430. 

Reactions  to  stimuH,  35,  43,  56,  114. 

Reactiveness,  10. 

Recapitulation,  302. 

Rectrices,  576,  579. 

Rectum,  638. 

Redia,  159,  160. 

Reduction  of  chromosomes,  82,  85. 

Rcduviidce,  348. 

Reflex,  225. 

Regeneration,  of  Amphibia,  523;  cray- 
fish, 289;  earthworm,  230;  echino- 
derms,  198,  201,  208;  Hydra,  117; 
Planaria,  155. 

Reindeer,  669,  683. 

Remora,  444,  467. 

Renal  portal  system,  425,  426,  488,  289. 

Renilla,  140. 

Reproduction,  asexual,  80;  budding,  80; 
fission,  80;   sexual,  79. 

Reproduction  of,  Ameba,  32,  33;  Cteno- 
phora,  148;  Euglena,  ^2,  ^\;  Grantia, 
96;  Hydra,  115;  Hydrozoa,  tit, 
Metridium,  136 ;  Mollusca,  271-272 ; 
Obelia,  121;  Paramecium,  59;  Pro- 
tozoa, 69;   sponges,  103. 

Reproductive  system  of,  Amphioxus,  399 ; 
Ascaris,  170-172;  crayfish,  287-289; 
earthworm,  226,  227,  228;  EnteroP- 
neusta,  387,  388;  frog,  490,  491-492; 
Gonionemus,  123;  honey-bee,  322-324; 
Hydra,  109,  no;  leech,  239;  liver 
fluke,  158;  mussel,  250;  perch,  441; 
pigeon,  586;  Planaria,  152,  153; 
rabbit,   640-641;    snail,   257;    spider, 


INDEX 


727 


373,  376 ;    squid,  265,   267 ;    starfish, 
197;  tapeworm,  163, 164 ;  vertebrates, 

413. 

Reptantia,  297,  298. 

Reptilia,  401,  527-574,  694,  695;  classi- 
fication, 534-539;  economic  impor- 
tance, 570-571;  poisolnous,  569-570; 
prehistoric,  572-574;  review  of  orders 
and  families,  540-569. 

Respiration,  external,  407  ;  internal,  407  ; 
of  Ameha,  31;  coelenterates,  143; 
earthworm,  223;  echinoderms,  197, 
204,  206 ;  Grantia,  96 ;  leech,  238 ; 
mussel,  248;    rotifer,  182. 

Respiratory  system,  78;  of  Amphioxus, 
397;  crayfish,  284;  dogfish,  425;  fish, 
451-452;  frog,  482;  honey-bee,  319, 
320;  insects,  334;  perch,  438; 
pigeon,  585 ;  rabbit,  639 ;  snail,  255 ; 
spider,  373,  374;  turtle,  532;  verte- 
brates, 407. 

Respiratory  tree,  206,  207. 

Retina,  412,  505. 

Rhabdites,  155. 

Rhabdoccelida,  156. 

Rhabdo pleura,  387,  389. 

Rhacianectes,  675. 

Rhagodes,  382. 

Rhagon,  sponge,  99,  100. 

Rhampholeon,  537,  550. 

Rhamphorhynchus,  574. 

Rhea,  589,  596 ;  Rheiformes,  589,  596. 

Rheotropism,  36,  58. 

Rhineura,  557. 

Rhinoceros,  644,  671,  672;  Rhinocerotida, 

671, 
•  Rhinolophidcz,  651. 

Rhino phrynus,  512. 

Rhiptoglossi,  536,  550. 

Rhizopoda,  27-41. 

Rhodites,  366. 

Rhopalocera,  351. 

Rhopalura,  176. 

Rhynchocephalia,  527,  536,  546,  694,  695. 

Rhynchophora,  364. 

Rhynchops,  609. 

Rhynchotus,  597. 

Rhytina,  673. 

Ribs,  436,  636;   false,  405  (see  skeleton). 

Roccus,  465,  466. 

Rodentia,  643,  658-660,  688-689. 

Roller,  591,  610. 


Rorqual,  675. 
Rossia,  268. 
Rostrum,  277,  278. 
Rotatoria,  1 81-183. 
Rotifera,  181,  182,  183. 
Ruminant,  668. 
Rupicapra,  671. 

Sabella,  236. 

Saccidina,  294,  300. 

Sacculus,  411. 

Sacrum,  582  (see  skeleton). 

Sagitta,  180,  181. 

Sakis,  664. 

Salamanders,  477,  511,  514-517. 

Salamandra,  511,  516,  524,  525;    Sala- 

mandridce,    511,    515-516;    Salaman- 

droidece,  511. 
Salientia,  477,  511,  517-522,  694. 
Salmo,  460. 

Salmon,  443,  444,  459,  461,  475,  476. 
Salmonidce,  444,  459, 
Salpa,  393. 
Salvelinus,  460. 
Sand,   dollar,  205 ;    -hopper,  296,  301 ; 

-piper,  607. 
Saperda,  363. 
Sapphirina,  294. 
Saprophytic  nutrition,  43. 
Sapsusker,  614. 
Sarcopsylla,  360. 
Sarcopte's,  381. 
Sarcorhamphus,  604, 
Sarcbsporidia,  53. 
Sarcosystis,  53. 
Sauria,  537,  551. 
Scale  insects,  345,  346,  347. 
Scales,  cycloid,  435,  448;    ctenoid,  435, 

448 ;    dermal,  433  ;    ganoid,  435,  448  ; 

of   mammals,    676;     of   pigeon,    577; 

placoid,  424. 
Scallops,  263. 
Scalops,  649. 

Scaphiopus,  512,  518,  519. 
Scaphirhynchus,  453. 
Scaphognathite,  277,  279. 
Scaphopoda,  243,  261. 
Scapula,  404,  495,  496. 
ScarabceidcB,  361 ;  Scarabeus,  362. 
Sceloporus,  537,  555. 
Schistosoma,  168. 
Scincidce,  538,  557. 


728 


INDEX 


SciuridcB,  658. 

Scinropterus,  659. 

Sciurus,  643,  658. 

Sclerite,  330. 

Sclerotic,  coat,  411,  412;  plates,  587, 

Scolex,  163. 

Scolopendrella,  311. 

Scolytid(B,  364. 

Scomber,  468,  469. 

Scomberomorus,  469. 

Scombrida,  444,  468. 

Scorpion,  24,  275,  377-379- 

Scorpionidca,  377-379. 

Screamer,  590,  603, 

Scrotal  sacs,  640. 

Scutellum,  330. 

Scutigera,  311. 

Scutum,  330. 

Scyllium,  427. 

Scyphozoa,  108,  129-133. 

Sea,  -anemone,  134;  -bass,  444;  -cow, 
645,673;  -cucumber,  205-208 ;  -horse, 
444,  465;  -lily,  190,  208;  -lion,  643, 
656;  -squirt,  390;  urchin,  189,  202; 
walnut,  23, 145. 

Seals,  643,  657,  658. 

Secretion,  31 ;  internal,  492. 

Segmentation,  homonomous,  91 ;  heter- 
onomous",  91. 

Selachii,  428-430. 

Seminal  receptacle,  217  (see  reproduc- 
tive system). 

Seminal  vesicle,  227  (see  reproductive 
system). 

Sense  organs,  of  Aurelia,  130,  131 ;  cray- 
fish, 285;  Ctenophora,  145,  147,  148; 
earthworm,  226;  dogfish,  427;  frog, 
504-506;  honey-bee,  321-322;  lam- 
prey, 418;  mussel,  249;  Nereis,  234; 
perch,  440;  pigeon,  587;  rabbit,  640; 
snail,  256;  squid,  267;  starfish,  197; 
turtle,  533 ;   vertebrates,  410-413. 

Septa,  of  coral  polyp,  137;  earthworm, 
218. 

Septibranchia,  262. 

Serpcntes,  538,  557-569,  694,  695. 

SerranidcE,  444,  465. 

Serricornia,  361. 

Sertularia,  122,  128. 

Serum,  484. 

Setae,  of  earthworm,  216,  217;  penial,  of 
Ascaris,  169,  171. 


Shag,  602. 

Shagreen,  424. 

Sharks,  428-429,  431. 

Shearwater,  600. 

Sheep,  667,  669,  684. 

Shells,  of  Brachiopoda,  185 ;  mussel,  244 ; 

pigeon's  eggs,  586 ;   squid,  265,  266. 
Shields,  528,  544. 
Shrews,  642,  649,  650. 
Shrike,  591. 
Shrimp,    299,    301 ;     fairy-,    293,     299 ; 

mantis-,  301. 
Silenia,  262. 

Silpha,  361 ;  Silphi4(B,  361. 
Silurian,  697. 
SiluridcB,  443,  457-458. 
Simla,  644,  665 ;   Simiidce,  662,  664-666, 

696. 
SimpUcidentata,  643. 
Simuliidce,  357. 

Sinus,  194,  282  (see  circulatory  system). 
Sinus  venosus,  438,  485  (see  circulatory 

system). 
Siphon,   of   mussel,   244,   245,   247;     of 

sea   urchin,  203,   204;    of   Sycotypus, 

261. 
Siphonaptera,  337,  359-360. 
Siphonoglyphe,  134,  135. 
Siphonophora,  125,  129. 
Siphonops,  510. 
Siphuncle,  268,  269. 
Sipunculoidea,  187 ;  Sipunculus,  187. 
Siren,  477,  511,  514;   Sirenida,  511,  514. 
Sirenia,  645,  673-674. 
Sistrurus,  569. 
Sittida,  591. 
Skates,  429,  430. 
Skeleton,   78,   403;    dogfish,   424;    fish, 

449 ;    frog,    492-497  ;    lamprey,   416 ; 

perch,  434-437 ;    pigeon,  579;    rabbit, 

634-637 ;       sea-urchin,      202,       203 ; 

sponges,  99,  loi ;    starfish,   191,  192, 

195;  turtle,  528. 
Skimmer,  607,  609. 
Skin,  479. 
Skink,  538,  557. 
Skipper,  350,  351. 
Skua,  608. 
Skunk,  643,  655. 
Skull,  312,  403  (see  skeleton). 
Sloth,  643,  661. 
Smell  (see  sense  organs). 


INDEX 


729 


Smilisca,  519. 

Snail,  253-257. 

Snakes,    527,    536,    538-539,  "557-569 

Congo,  514;   horsehair,  179. 
Snipe,  590,  607. 
Sole,  469.  « 

Solen,  262. 
SolenodonlidcB,  650. 
SolifugcB,  382. 
Somatic,   cells,   46,  47,  73;    mesoderm, 

507. 
Somite,  90. 
Songs  of  birds,  621. 
Sorex,  642,  649,  650 ;  Soricida,  649. 
Sparrow,  593,  615. 
Spatangus,  190. 
Species,  22,  23. 
Spelerpes,  511,  517/ 
Spermatheca,  226,  227  (see  reproductive 

system).  ' 

Spermatid,  81. 
Spermatocytes,  81. 
Spermatogenesis,  81-82. 
Spermatogonia,  81. 
Spermatozoa,  47,  75,  81. 
Sphcerodactylus,  537,  552. 
Sphcerophyra,  65. 
Sphargis,  544. 
SphegidcB,  364,  367. 
Sphenethmoid,  493,  494. 
Spheniscus,   589;    Spftenisciformes,   589, 

598. 
Sphenodon,  536,  546,  695. 
Sphingidce,  352  ;  Sphinx,  335. 
Sphyranura,  161. 
Sphyrna,  429. 

Spicules,  of  sponges,  93,  95,  99,  191. 
Spiders,  24,  371-377- 
Spilogale,  655. 
Spinal  cord,  408,  503-504  (see  nervous 

system) . 
Spinal    nerves,    503,    504    (see    nervous 

system). 
Spines,  of  echinoderms,   190,  201,  292; 

haemal,  436;   of  perch,  435. 
Spinneret,  373,  376. 
Spiracle,  insects,  319,  320;  Squalus,  424; 

tadpole,  510. 
Spiral  valve,  418,  423,  425, 
Spireme,  15. 
Spirobolus,  310. 
Spirorbis,  236. 


Spirostomum,  63. 

Spittle  insects,  346. 

Splanchnic  mesoderm,  507. 

Spleen,  451 ;  frog,  492;  perch,  438;  ver- 
tebrates, 401,  402. 
'Sponges,  23,  92-107. 

Spongilla,  98,  98,  100. 
•Spongin,  99,  loi. 

Spongoblasts,  100. 

Spontaneous  generation,  12. 

Spores,  48,  49. 

Sporoblast,  49,  50. 

Sporocyst,  159,  160. 

Sporozoa,  27,  48-53. 

Sporozoites,  49,  50. 

Sporulation,  33. 

Springtails,  337,  338. 

Squali,  428. 

Squalus,  422-428. 

Squamata,  527,  536,  550-569,  694,  695. 

Squamosal,  493,  494. 

Squid,  264-267. 

Squilla,  298,  299,  301. 

Squirrel,  643,  658,  659. 

Staphylinidce,  361. 

Starfish,  24,  i8p,  190-199. 

Starling,  591. 

Statocyst,  286  (see  sense  organs). 

Statolith,  286  (see  sense  organs). 

StauromeduscB,  132,  133. 

Staurotypus,  535. 

Stegocephalia,  525,  526,  694,  695. 

Stegomyia,  356. 

Stegosaurus,  572,  573. 

Stenopus,  297. 

Stentor,  64. 

Stercoral  pocket,  373,  374. 

Stereolepis,  466. 

Sternothoerus,  535. 

Sternum,  276,  372,  495,  496  (see  skele- 
ton). 

Stickleback,  444,  464. 

Stigma,  42,  43. 

Stigmata,  378,  379. 

Stilt,  607. 

Sting,  317. 

Stolonifera,  139,  140. 

Stomach,  cardiac,  480;   pyloric,  481  (see 
digestive  system). 

Stomato-gastric  ganglion,  321. 

Stomatopoda,  297,  298. 

Stomias,  473. 


730 


INDEX 


Stomodaeum,  Ctenophora,  146,  147  ;  frog, 

508;   Metridium,  134,  135;  Scyphozoa, 

132. 
Stork,  601, 
Streptoneura,  258. 
StrigidcB,  591,  611. 
Strobilization,  131,  132,  163. 
StrongylidcE,  173. 
Strongylocentrotus,  190,  202. 
Struthio,  589,  595 ;  Struthioniformes,  589, 

595- 
Sturgeon,  443,  453-454,  475- 
Sturnida,  591. 
Slylochus,  157. 
Stylonychia,  64. 
Stylotella,  102. 
Subcosta,  333. 
Submentum,  313. 
Submucosa,  481. 
Sub  terrestrial,  7. 
Subumbrella,  123. 
Sucker,  443,  456,  475  ;  of  liver  fluke,  157, 

158;   tadpole,  508;   tapeworm,  163. 
Sudor ia,  64,  65. 
Siiidcr.,  667. 
Sulci,  639. 
Sunfish,  467. 
Suprarenals,  428,  451. 
Suprascapular,  495,  496. 
Sus,  644,  671,  685. 
Suspensory  ligament,  412. 
Swallow,  591,  615. 
Swan,  590,  603,  631. 
Swarming,  of  bees,  327. 
Swifts,  555,  591,  613. 
Swimmerets,  277,  278,  281. 
Swordfish,  444. 
Sycon,  96,  97,  99,  100. 
Sycotypus,  258,  260,  261. 
SylviidcB,  591. 
Sylvilagus,  658. 
SymbranchidcB,   444 ;    Symbranchiformes, 

444;  Symbranchii,  444. 
Symmetry,    bilateral,    15,  90,   167,  401; 

biradial,  145,  146;   radial,  90. 
Sympathetic  nervous  system,   503,    504 

(see  nervous  system). 
Sym phyla,  311. 
Syngamus,  173. 

SyngnathidcB,  444,  465 ;  Syngnathus,  465. 
Syrinx,  585. 
SyrphidcB,  359. 


Syrrophus,  520. 
Systemic  heart,  266. 

TabanidcB,  358. 

Tadpoles,  509. 

Tcenia,  163,  166,  i68._. 

Tails,  of  birds,  617-618;  of  fish,  445,  446, 

447;   of  Rotifera,  181,  182. 
Talorchestia,  296,  297. 
TalpidcE,  649. 

Tanager,  593 ;  Tanagrida,  593. 
Tanaidacea,  296,  297. 
Taniilla,  539. 
Tapeworm,  163,  166,  168. 
Tapir,  644,  671,  672 ;  Tapirida,  671,  672 ; 

Tapirus,  644,  672. 
Tardigrada,  384,  385. 
Tarentola,  552. 
Tarpon,  444,  458. 
TarsiidcB,  662. 
Tarso-metatarsus,  580,  582. 
Tarsus,  314,  315,  372,  497. 
Tasmanian  devil,  649. 
Taste,  637  (see  sense  organs). 
Tatusia,  643,  66i. 
Taxidea,  655. 
Taxonomy,  26. 

Tayassu,  668;  TayassuidcE,  667,  668. 
Teat,  634. 

Teeth,  403,  678-680;   carnassial,  652. 
Tegmina,  334. 
Tciida,  538. 
Telea,  353. 

Teleostei,  443,  455-471,694,  695.  . 
Teleostomi,  432,  443,  452. 
Telophase  of  mitosis,  15,  16. 
Telosporidia,  52. 
Telson,  277. 
Tendon,  495. 

Tenebrio,  363  ;  Tenebrionida,  363. 
Tenrecs,  650. 
Tentacles,  oi  Ampkioxus,  sg6;  Brachiop- 

oda,  186 ;  Bugula,  184 ;  Ctenophora,.  146 ; 

Gonionemus,    123;    Hydra,    109,    no; 

Loligo,  264,  265  ;  Metridium,  134,  135  ; 

Obiiia,  120,  121;    sea  cucumber,  205, 

206,  207;   tunicates,  391. 
Tentaculocysts,  131,  132. 
TettthredinidcE,  365. 
Teratology,  26. 
Terebella,  236. 
Teredo,  262,  263,  264. 


INDEX 


731 


Tergum,  276,  277,  330. 

Termes,  340;  Termites,  340. 

Tern,  590,  607,  608. 

Terrapene,  542. 

Terrapines,  541,  542,  571. 

Terricola,  236. 

Tessera,  132,  133.  ' 

Test,  of  sea  cucumber,  202,  203;    tuni- 

cates,  390. 
Testes,     490,     491      (see     reproductive 

system) . 
Testudinata,  527,  534-536,  540-546;  694, 

695- 
TestudinidcB,  535,  541 ;  Testudo,  535,  543. 
Tetrahranchia,  268. 
Tctraopes,  363. 
Tctrastemma,  177. 
Tetraxonida,  105. 
Thalassicolla,  40. 
Thalassochelys,  543. 
Thalessa,  367. 
Thaliacea,  390,  393. 
Thamnophis,  539,  560,  561. 
Theca,  of  polyp,  137. 
Thecocystis,  209. 
Tliecoidea,  209,  210,  213. 
T her idida,  2,77 ',  Theridium,  yj6. 
Theromorpha,  694,  695. 
Thermotropism,  36,  37. 
Thigmotropism,  36,  57,  228,  291. 
ThomisidcB,  377  ;  Thomisus,  376. 
Thorax,  314,  329. 
Thrasher,  591. 
Thrips,  342. 
Thrush,  591. 
Thunnus,  469. 
Thylacomys,  642. 
ThylacynidcB,  649. 
Thymus,  451,  492. 
Thyone,  190,  206,  207. 
Thyrohyals,  493,  495. 
Thyroid,  451,  492. 
Thyropterida,  651. 
Thysanoptera,  337,  342. 
Tibia,  314,315,  372,404. 
Tibiale,  404,  497. 
Tibio-fibula,  497. 
Tibiotarsus,  580,  582. 
Ticks,  24,  275,  337,  359,  380. 
Tiger,  656. 

Tinamous,  589,  596,  597;  Tinamus,  589. 
Tinea,  355;  Tineidce,  355. 


Tipulidce,  356. 

Tissues,  74,  75,  76, 

Titmouse,  591. 

Toads,   477,    512,    517,    518,    519,   522; 

homed,  555. 
Tomicus,  364. 
Tomistoma,  548. 

Tongue,  480  (see  digestive  system) 
Tonsil,  637. 

Tornaria,  214,  388,  389,  693. 
TorpedinidcB,  430. 
Tortoises,  527,  534,  54°,  543- 
Tortoise-shell,  544,  571. 
TortricidcB,  355. 
Torus,  677. 
Toucan,  610. 
Toxopneustes,  82,  190. 
Tracheae,    of    insects,    319,    320,    373 ; 

Peripatus,  308;    pigeon,  585;    rabbit, 

639. 
Tracheata,  275. 
Trachydermon,  252. 
TrachymeduscB,  128. 
Trachynema,  128. 
Tragulidce,  667;  Tragulus,  671. 
Transverse  process,  402,  404,  493,  495. 
Tree  hoppers,  346. 
Trematoda,  150,  157-162. 
Trepang,  208. 
Trial  and  error,  115. 
Triarthrus,  293,  299. 
Triassic,  697. 

Trichinella,  173,  174;    TrichineUidce,  173. 
Trichinosis,  173. 
Trichocysts,  53,  54. 
Trichoptera,  337,  350. 
Tricladida,  152,  156. 
Trilobita,  292,  293,  299. 
Trimera,  363. 
Trionychidce,    536,    545;     Trionychoidea, 

536. 
Trionyx,  536,  545. 
Triploblastic,  89. 
Triton,  511,  515,  516,  524. 
Trituberculata,  685. 
Trochanter,  314,  315.  372. 
Trochilidce,  591,  612;  Trochilus,  613. 
Trochocystis,  209. 
Trochophore,  of  Echiiiroidea,  187;   mol- 

lusks,  271,  272  ;   Polygordius,  232,  233, 

241 ;  Rotifera,  183. 
Trochosphere  (see  trochophore). 


732 


INDEX 


Troglodytes,  615. 

J'roglodytidcB,  591. 

Trogon,  610. 

Trombidiidce,  380. 

Tropaa,  354. 

Trophoblast,  680. 

Trophozoite,  49,  50. 

Tropism,  35,  36. 

Trout,  443,  444,  459,  460,  475,  476. 

Truncus  arteriosus,  485  (see  circulatory 

system). 
Trypanosoma,  70. 
Trypsin,  482. 
Tube-feet,  191,  192,  193,  194,  197,  200, 

202,  204,  206. 
Tubifex,  236. 
Tubipora,  139,  140. 
Tubularia,  128. 
Tubulidentata,  644. 
Tuna,  469. 

Tunicata,  386,  389-393,  691,  296,  693. 
Tupaiidce,  650. 
Turbellaria,  150,  155-157. 
Turbot,  469. 
Turdidce,  591. 
Turkey,  590,  606,  631. 
Turnstone,  607. 
Turtles,   527-534;    535,   536,   540,   541, 

542,  543,  544,  571. 
Tympanic  membrane,  478,  640. 
Tympanuchiis,  606. 
Typhlomolge,  511,  513,  5i4- 
TyphlopidcB,  538 ;  Typhlops,  538. 
Typhlosole,  216,  219,  418. 
Typhlotriton,  517. 
TyrannidcB,  591,615,616;  Tyrannus,  615. 

Uca,  302. 

Uintatherium,  686. 

Ulna,  404. 

Ulnare,  404,  496,  497. 

Umbo,  244. 

Uncinate  process,  579,  580. 

Ungalia,  539. 

Unguiculata,  632,  642. 

Ungulata,  633,  644. 

Unio,  243  (see  Anodonta). 

Ureters,     407,     490     (see     urinogenital 

system) . 
Urethra,  640. 
Urine,  639. 
Uriniferous  tubules,  491, 


Urinogenital    system,    of    dogfish,    428; 

lamprey,  417,  419;   turtle,  532,  533. 
Urnaklla,  185. 
Urochorda,  389. 
Urocyon,  653. 
Urodela,  510. 
Uroglena,  45. 
Uropod,  278,  281. 
Urosalpinx,  258,  260. 
Urostyle,  493,  495. 
Ursidce,  652,  654. 
Ursus,  654,  655. 
Uta,  555. 
Uterus,  490,  492,  641  (see  reproductive 

system) . 
Uterus  masculinus,  640. 
Utriculus,  411. 

Vacuole,  13;  contractile,  28,  29,  42,  53, 
54;  food,  28,  30. 

Vagina,  322,  323  (see  reproductive 
system). 

Vampire  bat,  643,  651. 

Varanidce,  537  ;  Varanus,  537. 

Vas  deferens,  226,  227  (see  reproductive 
system). 

Vas  eflferens,  490,  491 . 

Veins,  487,  485,  489  (see  circulatory 
system) . 

Veliger,  271. 

Velum,  123,  271,  396,  397. 

Vena  cava,  247  (see  circulatory  system). 

Ventricle,  406,  486  (see  circulatory  sys- 
tem). 

Ventriculus,  334,  335. 

Venus,  262. 

Venus',  flower  basket,  103,  106;  girdle, 
147. 

Vertebrae,  amphicoelous,  435 ;  caudal,  405, 
636 ;  cervical,  405,  636 ;  dorsal,  405 ; 
lumbar,  636 ;  procoelous,  495 ;  sacral, 
405,  636;    thoracic,  636. 

Vertebral  column,  400,  404,  493,  495 
(see  skeleton). 

Vertebrates,  24,  400-701 ;  circulatory 
system,  406 ;  classes  of,  400 ;  digestive 
system,  405 ;  excretory  system,  407 ; 
integument,  402,  403 ;  muscular  sys- 
tem, 405  ;  nervous  system,  408 ;  plan 
of  structure,  401 ;  reproductive  system, 
413  ;  respiratory  system,  407  ;  skele- 
ton, 403-405  ;    sense  organs,  410. 


INDEX 


733 


Vespa,  368,  369 ;  VespidcE,  364,  368. 

Vespertilio,  651. 

Vestibule,  394,  395- 

Vibrissae,  634. 

Viceroy  butterfly,  352. 

Villi,  406. 

Vinegar-eel,  169. 

Viper,  539,  565  ;  Vipera,  539 ;  Viperidce^ 
539,  565 ;    Viperince,  539,  565. 

Vireo,  591 ;  Vireonida,  591. 

Viverridce,  653. 

Viviparous,  Sp^  413. 

Visceral  skeleton,  493,  494-495  (see  skele- 
ton). 

Vision,  286  (see  sense  organs). 

Vocal,  cords,  483,  639;  sacs,  484. 

Volvox,  46. 

Vomer,  493,  494. 

Vorticella,  64,  65. 

Vulpes,  653. 

Vultiu-e,  590,  603,  604. 

Wagtail,  591. 

Waldheimia,  186. 

Walking-stick,  343,  344, 

Wallaby,  642,  648. 

Walrus,  657. 

Wapiti,  669. 

Warbler,  591,  593. 

Wasps,  364,  367,  368. 

Water,  moccasin,  565,  566 ;  striders,  348 ; 

vascular  system,  193,   200,    205,    206, 

207. 
Wax,  glands,  317  ;  pinchers,  315,  316. 
Waxwing,  591,  615. 
Weasel,  655. 

Web,  of  spider,  375,  377'. 
Web-foot,  of  frog,  479;  turtle,  528. 
Weevils,  362,  364. 
Whalebone,  674,  675. 
Whales,  645,  674-676. 
W^himbrel,  607. 


Whippoorwill,  612. 

Whitefish,  444,  459-460,  475,  476. 

Wildcat,  656. 

Windpipe,  585  (see  trachea). 

Wings,  bastard,  576,  582 ;  of  birds,  616- 

617;    honey-bee,    316;    insects,    333; 

pigeon,  576,  577. 
Wishbone,  580,  581. 
Wolf,  22,  653. 
Wolverine,  656. 
Wombat,  649. 
Woodchuck,  658,  659,  683. 
Woodcock,  607. 
Woodpecker,  591,  610,  614. 
Worms,  353,  354,  363  ;  bladder-,  164, 165  ; 

hook-,  175;  thread-,  24. 
Wren,  591,  615,  628;  tit,  591. 
Wryneck,  610. 

J^enopus,  512. 

Xiphias,  469 ;  Xiphiidce,  444,  469. 
Xiphisternima,  495,  496. 
Xiphosura,  383. 

Yak,  671. 

Yellow,  fever,  356 ;  -jacket,  368. 

Yoldia,  262. 

Yolk,  plug,  507,  508;  sac,  442. 

Zalophus,  643,  657. 
Zamenis,  539,  561. 
Zebra,  644,  671,  701. 
Zenaidura,  609. 
Zoa;a,  304. 
Zoantharia,  141. 
Zoanthidea,  142. 
Zocecium,  184. 
Zoogeography,  26. 
Zoology,  25,  26. 
Zoothamnium,  65. 
Zygapophysis,  493,  495. 
Zygote,  49,  50. 


'T^HE  following  pages  contain  advertisements  of 
-*•    books  by  the  same  author  or  on  kindred  subjects. 


An  Introduction  to  Zoology 

By   ROBERT   W.    HEGNER,  Ph.D. 

Instructor  in  Zoology  in  the  University  of  Michigan 


Illustrated,  i2mo,  $i.go  net 

Only  a  few  animals  belonging  to  the  more  important  phyla,  as  viewed 
from  an  evolutionary  standpoint,  are  considered.  They  are,  however,  inten- 
sively studied  in  an  endeavor  to  teach  the  fundamental  principles  of  Zoology 
in  a  way  that  is  not  possible  when  a  superficial  examination  of  types  from  all 
the  phyla  is  made.  Furthermore,  morphology  is  not  specially  emphasized,  but 
is  coordinated  with  physiology,  ecology,  and  behavior,  and  serves  to  illustrate 
by  a  comparative  study  the  probable  course  of  evolution.  The  animals  are 
not  treated  as  inert  objects  for  dissection,  but  as  living  organisms  whose 
activities  are  of  fundamental  importance.  No  arguments  are  necessary  to 
justify  the  "  type  course,"  developed  with  the  problems  of  organic  evolution 
in  mind,  and  dealing  with  dynamic  as  well  as  static  phenomena. 

"  I  have  read  your  chapter  (The  Crayfish  and  Arthropods  in  General)  and 
can  express  my  satisfaction  with  reference  to  the  general  arrangement  of  the 
matter,  as  well  as  with  reference  to  the  detail.  The  whole  treatment  is  up  to 
date,  taking  account  of  the  modern  advancement  in  our  knowledge  of  the 
crayfishes,  and,  chief  of  all,  the  more  important  features  in  the  natural  history 
of  these  animals  are  very  properly  separated  from  the  unimportant  ones.  I 
think  this  chapter  gives  the  essence  of  what  we  know  about  crayfishes,  and 
any  student  might  use  the  book  advantageously.  In  fact,  I  know  no  other 
text-book  which  gives  such  a  wealth  of  information  upon  so  few  pages."  — 
Professor  A.  E.  Orthmann,  Carnegie  Museum. 

"  The  plan  is  very  satisfactory,  and  the  book  will  be  very  instructive  for 
class  use.  I  am  very  glad  that  you  have  chosen  the  bee  as  your  insect  type." 
(Chapter  XII.) — Dr.  E.  E.  Phillips,  Department  of  Agriculture,  Washing- 
ton, D.C. 


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The  Age  of  Mammals  in 
Europe,  Asia,  and  North  America 

By  HENRY  FAIRFIELD  OSBORN 

A.B.,  Sc.D.  Princeton,  Hon.  LL.D.  Trinity,  Princeton,  Columbia,  Hon.  D.Sc. 

Cambridge  University,  Hon.  Ph.D.  University  of  Christiania, 

President  American  Museum  of  Natural  History, 

President  New  York  Zoological  Society 

Illustrated  by  232  Halftone  and  Other  Figures,  including 
Numerous  Maps,  Geological  Sections,  Field  Views,  and 
Reproductions  from  Photographs  of  Mounted  Fossil  Skele- 
tons and  of  the  Famous  Restorations  by  Charles  R.  Knight 

Decorated  clolh^  8vo,  $4.^0  net 

COMMENTS 

"  Students  of  palceontology  have  awaited  impatiently  the  past  few  years  a 
promised  work  on  extinct  mammals  by  Professor  Osborn.  In  his  '  Age  of 
Mammals,'  expectations  have  been  more  than  realized."  —  S.  W.  Williston, 
in  Science,  Feb.  17,  191 1. 

"  A  book  of  the  utmost  value  to  the  student  and  teacher  of  mammalian 
life  and  likewise  to  the  serious  reader."  —  American  Journal  of  Sciefice, 
Feb.,  191 1. 

"  M.  Osborn  ...  devait  s'attacher  a  nous  presenter  le  tableau  aussi 
complet  et  aussi  fldele  que  possible  des  faunes  de  Mammiferes  fossiles  qui  se 
sont  succede  dans  I'hemisphere  Nord  pendant  I'ere  tertiaire.  Et  j'ai  plaisir  a 
dire  tout  de  suite  qu'il  y  a  parfaitement  reussi."  —  M.  Boule,  in  Mouvement 
Scientijique,  1911,  p.  569. 

"  Professor  Osborn  has  produced  a  book  which  will  appeal  to  the  learned 
specialist  and  to  the  thoughtful  general  reader  as  well."  "The  work  is  well 
adapted  to  school  and  college  use,  and  is  abundantly  illustrated."  —  Educa- 
tion, Boston,  Jan.,  1911. 

"One  of  the  most  notable  books  on  evolution  since  the  appearance  of 
Darwin's  'Origin  of  Species.' "  —  Forest  and  Stream,  Dec.  10,  1910. 

"  Nejlepsi  soucasny  paloeontolog  americky,  Henry  Fairfield  Osborn,  vydal 
nedkvno  s  titulem  tuto  citovanym  znamenite  psanou  a  pekne  vypravenou 
knihu  o  *  veku  ssavcii.' "  —  F.  Bayer  in  Vestniku  Ceske  Akademie  cisare 
Frantilka  Josef  a  pro  vedy,  slovenost  a  umeni.  —  Rocnik  XX,   191 1. 


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From  the  Greeks  to  Darwin 

An  Outline  of  the  Development 
of  the  Evolution  Idea 

By  HENRY  FAIRFIELD 'OSBORN,  LL.D.,  D.Sc. 

Second  edition.     Cloih,  8vo,  2jo  pages,  $2.00  net 

The  Initial  Volume  of  the  "  Columbia  University  Biological  Series  " 

The  Anticipation  and  Interpretation  of  Nature.  —  Among  the 
Greeks.  —  The  Theologians  and  the  Natural  Philosophers.  — 
The  Evolutionists  of  the  Eighteenth  Century.  —  From  La- 
marck to  St.  Hilaire.  —  Darwin.  —  Index. 


"This  is  an  attempt  to  determine  the  history  of  Evolution,  its  development 
and  that  of  its  elements,  and  the  indebtedness  of  modern  to  earlier  investi- 
gators. The  book  is  a  valuable  contribution;  it  will  do  a  great  deal  of  good 
in  disseminating  more  accurate  ideas  of  the  accomplishments  of  the  present 
as  compared  with  the  past,  and  in  broadening  the  views  of  such  as  have  con- 
fined themselves  too  closely  to  the  recent  or  to  specialties.  ...  As  a  whole 
the  book  is  admirable.  The  author  has  been  more  impartial  than  any  of 
those  who  have  in  part  anticipated  him  in  the  same  line  of  work."  —  The 
Nation. 

"But  whether  the  thread  be  broken  or  continuous,  the  history  of  thought 
upon  this  all-important  subject  is  of  the  deepest  interest,  and  Professor 
Osborn's  work  will  be  welcomed  by  all  who  take  an  intelligent  interest  in 
Evolution.  Up  to  the  present,  the  pre-Darwinian  evolutionists  have  been  for 
the  most  part  considered  singly,  the  claims  of  particular  naturalists  being 
urged  often  with  too  warm  an  enthusiasm.  Professor  Osborn  has  undertaken 
a  more  comprehensive  work,  and  with  well-balanced  judgment  assigns  a  place 
to  each  writer."^ Prof.  Edward  B.  Poulton,  in  Nature,  London. 


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Evolution  of 
Mammalian  Molar  Teeth 

To  and  from  the  Triangular  Type 

Including  collected   and   revised  researches  on  trituberculy  and 

new  sections  on  the  forms  and  homologies  of  the 

molar  teeth  in  the  different  orders 

of  mammals 

By  HENRY  FAIRFIELD  OSBORN,  Sc.D.,  LL.D.,  D.Sc. 

Curator  of  Vertebrate  Palseontology  in  the  American 
Museum  of  Natural  History 

EDITED   BY 

W.  K.  GREGORY,  M.A. 
Lecturer  in  Zoology  in  Columbia  University 

Illustrated^  cloth^  8vo^  ix-\- 2^0  pages,  %2.oo  net 


"The  author  has  succeeded  in  placing  trituberculism  on  a  much  more 
secure  and  unassailable  basis  than  it  ever  previously  occupied."  —  Nature. 

"The  whole  book  gives  evidence  of  the  most  painstaking  work.  Perhaps 
its  most  delightful  feature  is  the  judicial  fairness  and  frankness  with  which 
the  whole  evidence  is  reviewed  and  discussed."  —  Science. 


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Publishers  64-66  Fifth  Avenue  New  York 


DATE  DUE  SLIP 

UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 

THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 

STAMPED  BELOW                                 i 

OCT  12  1938 

DEC  4    1939 

DEC  18  1939 
NOV  14  1940 

1 

JUL  2  5  ]y49 

AUG  9-1949 

3m-10,'34 

Library  of  the 
University  of  California  Medical  School  and  Hospitals 


